GNSS and optical guidance and machine control

ABSTRACT

A global navigation satellite sensor system (GNSS) and gyroscope control system for vehicle steering control comprising a GNSS receiver and antennas at a fixed spacing to determine a vehicle position, velocity and at least one of a heading angle, a pitch angle and a roll angle based on carrier phase position differences. The system also includes a control system configured to receive the vehicle position, heading, and at least one of roll and pitch, and configured to generate a steering command to a vehicle steering system. The system includes gyroscopes for determining system attitude change with respect to multiple axes for integrating with GNSS-derived positioning information to determine vehicle position, velocity, rate-of-turn, attitude and other operating characteristics. Relative orientations and attitudes between motive and working components can be determined using optical sensors and cameras. The system can also be used to guide multiple vehicles in relation to each other.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims the benefit of U.S.patent application Ser. No. 14/680,980, filed Apr. 7, 2015, now U.S.Pat. No. 9,141,111, issued Sep. 22, 2015, which is a continuation ofU.S. patent application Ser. No. 14/166,666, filed Jan. 28, 2014, nowU.S. Pat. No. 9,002,565, which is a continuation-in-part of U.S. patentapplication Ser. No. 13/426,395, filed Mar. 21, 2012, now U.S. Pat. No.8,639,416, which is a continuation-in-part of U.S. patent applicationSer. No. 12/857,298, filed Aug. 16, 2010, now U.S. Pat. No. 8,594,879,which is a continuation-in-part of U.S. patent application Ser. No.12/355,776, filed Jan. 17, 2009, now U.S. Pat. No. 8,140,223, which is acontinuation-in-part of U.S. patent application Ser. No. 12/171,399,filed Jul. 11, 2008, now U.S. Pat. No. 8,265,826, which is acontinuation-in-part of U.S. patent application Ser. No. 10/804,758,filed Mar. 19, 2004, now U.S. Pat. No. 7,400,956, which claims thebenefit of U.S. Provisional Patent Application No. 60/456,146, filedMar. 20, 2003 and No. 60/464,756, filed Apr. 23, 2003. This applicationis related to U.S. patent application Ser. No. 13/217,839, now U.S. Pat.No. 8,634,993. The contents of all of the aforementioned applicationsare incorporated by reference herein in their entireties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to machine control using globalnavigation satellite systems (GNSSs) and more particularly to anequipment control system and method.

2. Description of the Related Art

Movable machinery, such as excavators, graders, agricultural equipment,open-pit mining machines, aircraft crop dusters and other mobileoperating equipment can benefit from accurate positioning using globalnavigation satellite systems (GNSSs). For example, U.S. Pat. No.7,689,354, which is assigned to a common assignee herewith, disclosesagricultural equipment equipped with an adaptive guidance systemincluding a multi-antenna GNSS system for guidance, automatic steering,independent implement positioning and spraying control.

In the earth-moving field, a wide variety of equipment has been used forspecific applications, such as excavators, backhoes, bulldozers, loadersand motor graders. Earth-moving projects encompass a wide variety ofexcavating, grading, trenching, boring, scraping, spreading and othertasks, which are performed in connection with road-building,infrastructure improvements, construction, mining and other activities.Such tasks are typically performed by specialized equipment. Suchequipment can be relatively sophisticated and can handle relatively highcapacities of materials.

Mobile earth-moving equipment is steered and otherwise guided withinjobsites. Moreover, the working components of such equipment, such asblades, drills, buckets and ground-engaging tools, are controlledthrough their various ranges of motion. Machine guidance and controlwere conventionally accomplished by human operators, who often neededrelatively high levels of skill, training and experience for achievingmaximum production with the equipment. For example, jobsite grading wastypically accomplished by surveying the site, placing stakes atpredetermined locations to indicate the locations of “cutting” (i.e.earth removal) and “filling” (i.e. earth placement) operations requiredto achieve a final grading plan. Cut and fill quantities are preferablybalanced as much as possible to avoid added expenses for additional fillmaterial or removing excess material.

In addition to balancing material requirements, design parameters suchas water runoff, slope, compaction (relating to load-bearing capacity)and thicknesses of various material layers are important grading andsite design criteria. Previous earth-moving machinery tended to behighly reliant on operator skill for achieving desired final results.

The present invention uses satellite positioning systems (SATPSs), suchas the Global Positioning System (GPS) and other global navigationsatellite systems (GNSSs) for guidance and machine control. Projectbidding can thus be based on more precise labor, material quantity,fuel, equipment maintenance, material disposal, time and other costfactors. Project expenses can thus be reduced by controlling input costsof material, material hauling, fuel, labor, equipment utilization, etc.Still further, earth-moving operations that were previously conducted inseparate “rough” and “fine” phases can be combined into single-phaseprocedures due to the greater efficiencies and accuracies achievablewith the GNSS machine guidance and control of the present invention.Still further, operators tend to be less fatigued with a relatively highlevel of automated machine guidance and control, as opposed tomanually-intensive control procedures requiring high degrees ofconcentration and operator interaction.

Various navigation and machine control systems for ground-based vehicleshave been employed but each has disadvantages. Systems using Dopplerradar encounter errors with the radar and latency. Similarly,gyroscopes, which may provide heading (slew), roll, or pitchmeasurements, may be deployed as part of an inertial navigation package,but tend to encounter drift errors and biases and still require someexternal attitude measurements for gyroscope initialization and driftcompensation. Gyroscopes have good short-term characteristics butundesirable long-term drift characteristics, especially gyroscopes oflower cost such as those based on a vibrating resonator. Similarly,inertial systems employing gyroscopes and accelerometers have goodshort-term characteristics but also suffer from drift.

Providing multiple antennas on a vehicle can provide additional benefitsby determining an attitude of the vehicle from the GNSS ranging signalsreceived by its antennas, which are constrained on the vehicle at apredetermined spacing. For example, high dynamic roll compensationsignals can be output directly to the vehicle steering usingGNSS-derived attitude information. Components such as gyroscopes andaccelerometers can be eliminated using such techniques. Real-timekinematic (RTK) can be accomplished using relatively economical singlefrequency L1-only receivers with inputs from at least two antennasmounted in fixed relation on a rover vehicle. Still further, movingbaselines can be provided for positioning solutions involving machinecomponents and multi-vehicle/machine GNSS control.

GNSS-based equipment and methods can also be used for machine control,such as earth-moving equipment. GNSS guidance can provide a relativelyhigh level of accuracy. For instance, prior to GNSS guidance and machinecontrol, earth-moving operations tended to rely more on operator skillfor manually spot-checking grade elevations in order to smoothly cut andfill a plot of land to a particular height. With the GNSS guidance andmachine control of the present invention providing three-dimensional(3D) positional tracking, earth-moving equipment can perform cut, fill,and other earth-moving functions using GNSS positioning data for greaterrepeatable accuracy and operating efficiencies. Although GNSS-basedcontrol techniques have been used in earth-moving machinery, previousGNSS machine control systems used in such equipment do not provide theadvantages and features of the present invention.

By using GNSS-equipped earth-moving machines, the need for manual gradechecks can be reduced or eliminated on many grading projects. Slope andgrade measurements can be obtained with greater accuracy and qualitycontrol. Moreover, earth-moving jobs that were previously deemedchallenging and complex can be simplified, thus increasing the availablepool of qualified earth-moving contractors and equipment operators.GNSS-based guidance and control using the present invention can providemore information and control to the equipment operators, thus enablingthem to undertake more difficult tasks than they might have withmanually-controlled equipment and techniques. Consistency among operatorperformance can be improved via GNSS-based automation, resulting inbetter overall job quality. For example, relatively inexperiencedoperators can deliver results comparable to those achieved by moreexperienced operators using the information and automation features ofthe present invention. Another operator benefit relates to less fatigue,as compared to manually guiding and controlling the equipment and itsfunctions.

Profitability of earth-moving jobs using GNSS-equipped machines tends toimprove because bidding and execution risks are more highly controlled,input (e.g., material, material hauling, fuel and labor) costs can bereduced, the necessity of reworking projects in order to meetspecifications can be reduced, safety can be improved and equipment cancomplete more projects between service cycles due to greater operatingefficiencies.

Yet another application for GNSS-equipped machines involves snowmanagement, including snow grooming procedures for ski resorts.Maximizing use of available snow, both natural and man-made, is animportant aspect of managing winter sports areas, such as ski resorts.Effective snow grooming commonly involves relocating volumes of snow inorder to provide sufficient snow base depth, to cover obstacles and forconfiguring ski runs. Skiers often divert snow while making runs. Resortoperators often groom and reconfigure their ski runs after normaloperating hours to avoid interfering with daytime recreationalactivities. At many resorts grooming activities continue through thenight.

Snow grooming equipment operators are often exposed to hazardousconditions on the mountain, particularly when operating at night or inbad weather conditions. For example, blizzard conditions are oftenassociated with “white out” conditions restricting visibility. Operatingheavy equipment on steep, snow-covered terrain in limited visibility canbe hazardous to operators. Also, their procedures commonly requirerelatively precise navigation and positioning to avoid. Still further,snow base and snow depth control can be difficult without significantexperience and terrain knowledge.

Movable machinery, such as agricultural equipment, open-pit miningmachines, airplane crop dusters and the like all benefit from accurateglobal navigation satellite system (GNSS) high precision surveyproducts, and others. However, in existing satellite positioning systems(SATPS) for guided parallel and contour swathing for precision farming,mining, and the like, the actual curvature of terrain may not be takeninto account. This results in a less than precise production because ofthe less than precise parallel or contour swathing. Indeed, in order toprovide swaths through a field (in farming, for example), the guidancesystem collects positions of the vehicle as it moves across the field.When the vehicle commences the next pass through the field, the guidancesystem offsets the collected positions for the previous pass by thewidth of the equipment (i.e. swath width). The next set of swathpositions is used to provide guidance to the operator as he or shedrives the vehicle through the field.

The current vehicle location, as compared to the desired swath location,is provided to the vehicle's operator or to a vehicle's steering system.The SATPS provides the 3-D location of signal reception (for instance,the 3-D location of the antenna). If only 3-D coordinates are collected,the next swath computations assume a flat terrain offset. However, theposition of interest is often not the same as where the satellitereceiver (SR) is located since the SR is placed in the location for goodsignal reception, for example, for a tractor towing an implement, anoptimal location for the SR may be on top of the cab. However, theposition of interest (POI) for providing guidance to the tractoroperator may be the position on the ground below the operator. If thetractor is on flat terrain, determining this POI is a simple adjustmentto account for the antenna height.

However, if the tractor is on an inclined terrain with a variable tilt,which is often the case, the SATPS alone cannot determine the terraintilt so the POI also cannot be determined. This results in a guidanceerror because the POI is approximated by the point of reception (POR),and this approximation worsens as the terrain inclination increases.This results in cross track position excursions relative to the vehicleground track which would contaminate any attempt to guide to a definedfield line or swath. On inclined terrain, this error can be minimized bycollecting the vehicle tilt configuration along each current pass or theprevious pass. The swath offset thus becomes a vector taking the terraininclination into account with the assumption that from the first swathto the next one the terrain inclination does not change too much. It cantherefore be seen that there is a need for a better navigation/guidancesystem for use with a ground-based vehicle that measures and takes intoaccount vehicle tilt.

Various navigation systems for ground-based vehicles have been employedbut each includes particular disadvantages. Systems using Doppler radarwill encounter errors with the radar and latency. Similarly, gyroscopes,which may provide heading, roll, or pitch measurements, may be deployedas part of an inertial navigation package, but tend to encounter drifterrors and biases and still require some external attitude measurementsfor gyroscope initialization and drift compensation. Gyroscopes havegood short-term characteristics but undesirable long-termcharacteristics, especially those gyroscopes of lower cost such as thosebased on a vibrating resonator. Similarly, inertial systems employinggyroscopes and accelerometers have good short-term characteristics butalso suffer from drift. Various systems include navigating utilizingGNSS; however, these systems also exhibit disadvantages. Existing GNSSposition computations may include lag times, which may be especiallytroublesome when, for example, GNSS velocity is used to derive vehicleheading. As a result, the position (or heading) solution provided by aGNSS receiver tells a user where the vehicle was a moment ago, but notin real time. Existing GNSS systems do not provide high quality headinginformation at slower vehicle speeds. Therefore, what is needed is a lowcost sensor system to facilitate vehicle swath navigation that makes useof the desirable behavior of both GNSS and inertial units whileeliminating or reducing non-desirable behavior. Specifically, what isneeded is a means to employ low-cost gyroscopes (e.g., microelectromechanical (MEM) gyroscopes) which exhibit very good short-termlow noise and high accuracy while removing their inherent long-termdrift.

Providing multiple antennas on a vehicle can provide additional benefitsby determining an attitude of the vehicle from the GNSS ranging signalsreceived by its antennas, which are constrained on the vehicle at apredetermined spacing. For example, high dynamic roll compensationsignals can be output directly to the vehicle steering usingGNSS-derived attitude information. Components such as gyroscopes andaccelerometers can be eliminated using such techniques. Real-timekinematic (RTK) can be accomplished using relatively economical singlefrequency L1-only receivers with inputs from at least two antennasmounted in fixed relation on a rover vehicle. Still further, movingbaselines can be provided for positioning solutions involving tractorsand implements and multi-vehicle GNSS control can be provided.

Providing additional antennas in combination with standard SATPS andGNSS guidance, as mentioned above, along with optional gyroscopes is agreat method to increase GNSS positioning precision and accuracy, suchas is described in U.S. Patent Publication No. 2009/0164067 which isassigned to a common assignee and is incorporated herein. However,accuracy and precision can only improve the efficiency of workingvehicles, such as those in the agricultural field, to a limited extent.Although such systems are able to track and guide vehicles in threedimensions, including along ridges and sloped-regions, errors may appearin other aspects of a working vehicle. For example, in an agriculturalfield-working situation where a tractor is towing an implement, theimplement may slide on a sloped-region, or the tractor may list to oneside or another when entering softer soil or rocky areas. This canhappen repeatedly when a vehicle is guided around the same field,regardless of the precision of the guidance system in pre-planning apath. Thus, a system that can detect such changes in uniformity of afield as the vehicle traverses a path and remember those changes canpredict and re-route a more accurate and more economical path than aguidance system alone. Heretofore there has not been available a systemand method with the advantages and features of the present invention.

Heretofore there has not been available a GNSS-based guidance andcontrol system for agricultural, earth-moving and other equipment withthe advantages and features of the present invention.

SUMMARY OF THE INVENTION

Disclosed herein in an exemplary embodiment is a sensor system forvehicle steering control comprising: a plurality of global navigationsatellite systems (GNSSs) including receivers and antennas at a fixedspacing to determine a vehicle position, velocity and at least one of aheading (slew) angle, a pitch angle and a roll angle based on carrierphase corrected real time kinematic (RTK) position differences. The rollangle facilitates correction of the lateral motion induced positionerrors resultant from motion of the antennae as the vehicle moves basedon an offset to ground and the roll angle. The system also includes acontrol system configured to receive the vehicle position, heading, andat least one of roll, pitch and yaw, and configured to generate asteering command to a vehicle steering system.

Also disclosed herein in another exemplary embodiment is a method forcomputing a position of a vehicle comprising: initializing GNSS;computing a first position of a first GNSS antenna on the vehicle;computing a second position of a second GNSS antenna; and calculating aheading as a vector perpendicular to a vector joining the first positionand the second position, in a horizontal plane aligned with the vehicle.The method also includes computing a roll angle of the vehicle as anarc-tangent of a ratio of differences in heights of the first GNSSantenna and the second GNSS antenna divided by a spacing between theirrespective phase centers and calculating an actual position at thecenter of the vehicle projected to the ground using the computed rollangle and a known height from the ground of at least one of the firstGNSS antenna and the second GNSS antenna.

Further disclosed herein in yet another exemplary embodiment is a methodof controlling a vehicle comprising: computing a position and a headingfor the vehicle; computing a steering control command based on aproportionality factor multiplied by a difference in a desired positionversus an actual position, plus a second proportionality factormultiplied by a difference in a desired heading versus an actualheading, the second proportionality factor ensuring that when thevehicle attains the desired position the vehicle is also directed to thedesired heading, and thereby avoiding crossing a desired track. Themethod also includes a recursive adaptive algorithm employed tocharacterize the vehicle response and selected dynamic characteristics.

The method further includes applying selected control values to avehicle steering control mechanism and measuring responses of thevehicle thereto; calculating response times and characteristics for thevehicle based on the responses; and calibrating the control commands byapplying a modified control command based on the responses to achieve adesired response.

Additional alternative aspects include selective sprayer nozzle control,high dynamic roll compensation using GNSS attitude solutions frommultiple antennas, moving baseline implement positioning and multiplevehicle control.

An additional embodiment of the present invention includes employing theabove-mentioned multiple GNSS antenna guidance system on earth-movingequipment, such as an excavator, grader, bulldozer, loader or the like.GNSS guidance obtains three-dimensional positional and attitude(heading) data, including coordinates defined in relation to a geodesiccoordinate system and rotation about X, Y, and Z axes. The excavator isalso modified with multiple sensors on the excavation arm (e.g.,“stick-and-boom”) or other such working implement. The GNSS guidancesystem computes the three-dimensional position of the bucket on theimplement arm by comparing the GNSS position of the excavation vehicleitself with the various angle sensors placed on the implement armholding the bucket. Using this combination, an excavator can preciselycut or fill a piece of land to a relatively precise desired elevationeither based on a pre-planned terrain map or by setting an initialelevation with the GNSS guidance system and computing the cut/fillquantities and locations from that base reference point or benchmark.

Still further alternative embodiments of the present invention areadapted for snow grooming operations and include equipment controlsubsystems mounted on snowcats, snowmobiles and other snow equipmentpieces.

An additional exemplary embodiment is a sensor system for vehicleguidance using one or more global navigation satellite systems (GNSSs)according to the above-mentioned embodiments, in combination with aplurality of various sensors located throughout a vehicle and a towedimplement. These sensors detect additional parameters from thosecalculated by the GNSS positioning system, such as vehicle and implementstress levels, fuel levels, power levels, optical guide pathobservations via an onboard camera, multi-section (articulated)implement position and attitude sensing via multiple antennas and othercharacteristics of the working vehicle. The combination of the twosystems results in a much more accurate and economical preplanned pathgenerated for use in later field work.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an illustrative diagram of a vehicle including anexemplary embodiment.

FIG. 2 depicts an illustrative block diagram of the vehicle including anexemplary embodiment of a sensor system.

FIG. 3 depicts an illustrative block diagram of a sensor system inaccordance with an exemplary embodiment.

FIG. 4 depicts an illustrative sensor system in accordance with anexemplary embodiment.

FIG. 5 depicts an illustrative flow chart of an exemplary process fordetermining a steering command for a vehicle in accordance with anexemplary embodiment.

FIG. 6 depicts an illustrative flow chart of an exemplary process fordetermining a steering command with an exemplary sensor system inaccordance with an alternative embodiment.

FIG. 7A depicts a multi-axis antenna and gyroscope system embodying anaspect of the present invention and including two antennas connected bya rigid link and yaw and roll gyroscopes.

FIG. 7B depicts the system in a yaw attitude.

FIG. 7C depicts the system in a roll attitude.

FIG. 8 depicts a tilt (roll) angle measuring application of theinvention on an agricultural vehicle.

FIG. 9 depicts an alternative aspect of the system with antenna andgyroscope subsystems mounted on both the vehicle and the implement, e.g.a sprayer with selectively controllable spray nozzles.

FIG. 10 depicts a block diagram of the system shown in FIG. 9.

FIG. 11 depicts a high dynamic roll compensation GNSS guidance systemcomprising an alternative aspect of the present invention.

FIG. 12 depicts a block diagram of the system shown in FIG. 11.

FIG. 13 depicts an alternative aspect of the present inventioncomprising a moving baseline GNSS system with the tractor and theimplement each mounting a respective antenna for a 1+1 antennaconfiguration.

FIG. 14 depicts an enlarged, fragmentary view thereof, particularlyshowing implement yaw and pitch movements in connection with the movingantenna-to-antenna baseline.

FIG. 15 depicts another moving baseline alternative aspect in a 2+1antenna configuration.

FIG. 16 depicts another moving baseline alternative aspect in a 2+2antenna configuration.

FIG. 17 depicts the 2+1 moving baseline system in a contour mode ofoperation with a multi-position tail.

FIG. 18 depicts a block diagram of the moving baseline system(s).

FIG. 19 depicts a multi-vehicle GNSS relative guidance system includingprimary and secondary rovers.

FIG. 20 depicts a block diagram of the system shown in FIG. 19.

FIG. 21 is an isometric diagram of an excavator with a GNSS machinecontrol system comprising another alternative embodiment of the presentinvention in an earthmoving equipment application, the excavatorincluding three axes and three rotational movements around the axes.

FIG. 22 is an isometric diagram of the excavator with a block diagram ofthe major components.

FIG. 23 is a vertical cross-section of a job site with the excavator,and showing volumes of earth to be cut or filled to reach a desiredelevation.

FIGS. 24A and 24B are phases I and II of a flowchart showing a method ofan embodiment of this invention.

FIGS. 24C and 24D are phases I and II of a flowchart demonstrating thesteps necessary to perform a task using macros according to theinvention.

FIG. 25 shows another alternative embodiment application of the controlsystem in a surface motor grader application.

FIG. 26 shows another alternative embodiment of the control system in asnow grooming equipment application.

FIG. 27 shows a snowcat equipped with the GNSS-based control systemembodying an aspect of the present invention and adapted for snowgrooming operations.

FIG. 28 is a screen view of a monitor located in a cab of the snowgrooming equipment, showing a graphical user interface (GUI) of thecontrol system.

FIG. 29 is another screen view of the monitor showing other aspects ofthe system's operation.

FIG. 30 shows another alternative embodiment application of the controlsystem in a draw line configuration.

FIG. 31 shows the system in a snow grooming application using radar formeasuring snow depth.

FIG. 32 shows contour guidelines overlaid on a point grid for use interrain modeling, including snow depths.

FIG. 33 shows a point depth interpolation on the point grid for use interrain modeling, including snow depths.

FIG. 34 is a vertical cross-section of a snow-covered area, particularlyshowing elevations of interest in connection with a snow groomingoperation.

FIG. 35 is a flowchart of a topography modeling method embodying anaspect of the present invention using approximation based on scaling(ABOS).

FIG. 36 shows another alternative embodiment application of the controlsystem for guiding ore trucks in a mining operation.

FIG. 37 shows yet another alternative embodiment of the presentinvention using optical targets and cameras for determiningtractor—implement attitude and orientation.

FIGS. 38 and 39 show crosshair displays indicating implement attitudeand orientation.

FIGS. 40-43 show square displays indicating tractor-implement attitudeand orientation.

FIGS. 44-47 show elliptical displays indicating tractor-implementattitude and orientation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS I. GNSS Introduction

Global navigation satellite systems (GNSSs) are broadly defined toinclude GPS (U.S.), Galileo (proposed), GLONASS (Russia), Beidou/Compass(China, proposed), IRNSS (India, proposed), QZSS (Japan, proposed) andother current and future positioning technology using signals fromsatellites, with or without augmentation from terrestrial sources.Inertial navigation systems (INS) include gyroscopic (gyro) sensors,accelerometers and similar technologies for providing outputcorresponding to the inertia of moving components in all axes, i.e.through six degrees of freedom (positive and negative directions alongX, Y and Z axes). Yaw, pitch and roll refer to moving component rotationabout these axes. Said terminology will include the words specificallymentioned, derivatives thereof and words of similar meaning.

Disclosed herein in an exemplary embodiment is a sensor system forvehicle guidance. The sensor system utilizes a plurality of GNSS carrierphase differenced antennas to derive attitude information, hereinreferred to as a GNSS attitude system. Moreover, the GNSS attitudesystem may optionally be combined with one or more rate gyro(s) used tomeasure turn, roll or pitch rates and to further calibrate bias andscale factor errors within these gyros. In an exemplary embodiment, therate gyros and GNSS receiver/antenna are integrated together within thesame unit, to provide multiple mechanisms to characterize a vehicle'smotion and position to make a robust vehicle steering control mechanism.

It is known in the art that by using a GNSS satellite's carrier phase,and possibly carrier phases from other satellites, such as WAASsatellites, a position may readily be determined to within millimeters.When accomplished with two antennas at a fixed spacing, an angularrotation may be computed using the position differences. In an exemplaryembodiment, two antennas placed in the horizontal plane may be employedto compute a heading (rotation about a vertical Z axis) from a positiondisplacement. It will be appreciated that an exemplary embodiment may beutilized to compute not only heading, but either roll (rotation about alongitudinal Y axis) or pitch (rotation about a lateral X axis)depending on the orientation of the antennas relative to the vehicle.Heading information, combined with position, either differentiallycorrected (DGPS or DGNSS) or carrier phase corrected real time kinematic(RTK) provides the feedback information desired for a proper control ofthe vehicle direction. Addition of one or more rate gyros furtherprovides independent measurements of the vehicle's dynamics andfacilitates vehicle steering control. The combination of GNSS attitudeobtained from multiple antennas with gyroscopes facilitates calibrationof gyroscope scale factor and bias errors which are present in low costgyroscopes. When these errors are removed, gyro rates are more accurateand provide better inputs for guidance and control. Furthermore,gyroscopes can now effectively be integrated to obtain roll, pitch andheading angles with occasional adjustment from the GNSS-derivedattitude.

Existing systems for vehicle guidance may employ separate gyros, andseparate GNSS positioning or attitude systems. However, such systems donot provide an integrated heading sensor based on GNSS as disclosedherein. Moreover, separate systems exhibit the limitations of theirrespective technologies as mentioned earlier. The exemplary embodimentsas described herein eliminate the requirements of existing systems forother means to correct for vehicle roll. Moreover, an implementation ofan exemplary embodiment also provides a relatively precise, in both theshort-term and the long-term, means of calculating heading and headingrate of change (turn rate).

Another benefit achieved by incorporating a GNSS-based heading sensor isthe elimination or reduction of drift and biases resultant from agyro-only or other inertial sensor approach. Yet another advantage isthat heading may be computed while the vehicle is stopped or movingslowly, which is not possible in a single-antenna GNSS based approachthat requires a vehicle velocity vector to derive heading. This can bevery important in applications where a vehicle has to turn slowly toalign with another path. During these slow turns the gyro can drift awaybut by adding the use of a dual antenna GNSS solution the orientation ofthe gyro can be continuously corrected. This also permits immediateoperation of a slow moving vehicle after being at rest, rather thanrequiring an initialization from motion. Yet another advantage of anexemplary embodiment is that a combination of the aforementioned sensorsprovides sufficient information for a feedback control system to bedeveloped, which is standalone and independent of a vehicle's sensors oradditional external sensors. Thus, such a system is readily maintainedas vehicle-independent and may be moved from one vehicle to another withminimal effort. Yet another exemplary embodiment of the sensor employsglobal navigation satellite system (GNSS) sensors and measurements toprovide accurate, reliable positioning information. GNSS sensorsinclude, but are not limited to GNSS, Global Navigation System (GLONAS),Wide Area Augmentation System (WAAS) and the like, as well ascombinations including at least one of the foregoing.

GNSS includes the Global Positioning System (GPS), which was establishedby the United States government and employs a constellation of 24 ormore satellites in well-defined orbits at an altitude of approximately26,500 km. These satellites continually transmit microwave L-band radiosignals in three frequency bands, centered at 1575.42 MHz, 1227.60 MHzand 1176.45 MHz, denoted as L1, L2 and L5 respectively. All GNSS signalsinclude timing patterns relative to the satellite's onboard precisionclock (which is kept synchronized by a ground station) as well as anavigation message giving the precise orbital positions of thesatellites. GPS receivers process the radio signals, computing ranges tothe GPS satellites, and by triangulating these ranges, the GPS receiverdetermines its position and its internal clock error. Different levelsof accuracies can be achieved depending on the techniques employed.

GNSS also includes Galileo (Europe), the GLObal NAvigation SatelliteSystem (GLONASS, Russia), Beidou (China), Compass (proposed), the IndianRegional Navigational Satellite System (IRNSS) and QZSS (Japan,proposed). Galileo will transmit signals centered at 1575.42 MHz,denoted L1 or E1, 1176.45 denoted E5a, 1207.14 MHz, denoted E5b,1191.795 MHz, denoted E5 and 1278.75 MHz, denoted E6. GLONASS transmitsgroups of FDM signals centered approximately at 1602 MHz and 1246 MHz,denoted GL1 and GL2 respectively. QZSS will transmit signals centered atL1, L2, L5 and E6.

In standalone GNSS systems that determine a receiver's antenna positioncoordinates without reference to a nearby reference receiver, theprocess of position determination is subject to errors from a number ofsources. These include errors in the GNSS satellite's clock reference,the location of the orbiting satellite, ionosphere induced propagationdelay errors, and troposphere refraction errors.

To overcome the errors of standalone GNSS systems, many positioningapplications have made use of data from multiple GNSS receivers.Typically, in such applications, a reference receiver, located at areference site having known coordinates, receives the GNSS satellitesignals simultaneously with the receipt of signals by a remote receiver.Depending on the separation distance between the two GNSS receivers,many of the errors mentioned above will affect the satellite signalsequally for the two receivers. By taking the difference between signalsreceived both at the reference site and the remote location, the errorsare effectively eliminated. This facilitates an accurate determinationof the remote receiver's coordinates relative to the referencereceiver's coordinates.

The technique of differencing signals from two or more GNSS receivers toimprove accuracy is known as differential GNSS (DGNSS or DGPS).Differential GNSS is well known and exhibits many forms. In all forms ofDGNSS, the positions obtained by the end user's remote receiver arerelative to the position(s) of the reference receiver(s). GNSSapplications have been improved and enhanced by employing a broaderarray of satellites such as GNSS and WAAS. For example, see commonlyassigned U.S. Pat. No. 6,469,663 to Whitehead et al. entitled Method andSystem for GNSS and WAAS Carrier Phase Measurements for RelativePositioning, dated Oct. 22, 2002, the disclosures of which areincorporated by reference herein in their entirety. Additionally,multiple receiver DGNSS has been enhanced by utilizing a single receiverto perform differential corrections. For example, see commonly assignedU.S. Pat. No. 6,397,147 to Whitehead titled Relative GNSS PositioningUsing a Single GNSS Receiver with Internally Generated DifferentialCorrection Terms, dated May 28, 2002, the disclosures of which areincorporated by reference herein in their entirety.

II. GNSS and Gyro Control System and Method

Referring now to FIGS. 1 through 4, an illustrative vehicle 10 isdepicted including a sensor system 20 in accordance with an exemplaryembodiment. Referring also to FIGS. 2 and 3, block diagrams of thesensor system 20 are depicted. The sensor system 20 includes, but is notlimited to a GNSS attitude system 22, comprising at least a GNSSreceiver 24 and an antenna 26. The GNSS receiver/antenna systemscomprising the GNSS attitude system 22 cooperate as a primary receiversystem 22 a and a secondary receiver system 22 b, with their respectiveantennas 26 a and 26 b mounted with a known separation. The primaryreceiver system 22 a may also be denoted as a reference or masterreceiver system, while the secondary receiver system 22 b may also bedenoted as a remote or slave receiver system. It will also beappreciated that the selection of one receiver as primary versussecondary need not be of significance; it merely provides a means fordistinguishing between systems, partitioning of functionality, anddefining measurement references to facilitate description. It should beappreciated that the nomenclature could readily be transposed ormodified without impacting the scope of the disclosure or the claims.

The sensor system 20 is optionally configured to be mounted within asingle enclosure 28 to facilitate transportability. In an exemplaryembodiment, the enclosure 28 can be any rigid assembly, fixture, orstructure that causes the antennas 26 to be maintained in asubstantially fixed relative position with respect to one another. In anexemplary embodiment, the enclosure 28 may be a lightweight bracket orstructure to facilitate mounting of other components andtransportability. Although the enclosure 28 that constrains the relativelocation of the two antennas 26 a and 26 b may have virtually anyposition and orientation in space, the two respective receivers 24(reference receiver 24 a and remote receiver 24 b) are configured tofacilitate communication with one another and resolve the attitudeinformation from the phase center of the reference antenna 26 a to thephase center of the remote antenna 26 b with a high degree of accuracy.

Yet another embodiment employs a GNSS sensor 20 in the embodiments aboveaugmented with supplementary inertial sensors 30 such as accelerometers,gyroscopes, or an attitude heading reference system. More particularly,in an implementation of an exemplary embodiment, one or more rategyro(s) are integrated with the GNSS sensor 20.

In yet another exemplary embodiment, a gyro that measures roll-rate mayalso be combined with this system's GNSS-based roll determination. Aroll rate gyro denoted 30 b would provide improved short-term dynamicrate information to gain additional improvements when computing the swayof the vehicle 10, particularly when traveling over uneven terrain.

It will be appreciated that to supplement the embodiments disclosedherein, the data used by each GNSS receiver 24 may be coupled with datafrom supplementary sensors 50, including, but not limited to,accelerometers, gyroscopic sensors, compasses, magnetic sensors,inclinometers, and the like, as well as combinations including at leastone of the foregoing. Coupling GNSS data with measurement informationfrom supplementary sensors 30, and/or correction data for differentialcorrection improves positioning accuracy, improves initializationdurations and enhances the ability to recover for data outages.Moreover, such coupling may further improve, e.g., reduce, the length oftime required to solve for accurate attitude data.

It will be appreciated that although not a requirement, the location ofthe reference antenna 26 a can be considered a fixed distance from theremote antenna 26 b. This constraint may be applied to the azimuthdetermination processes in order to reduce the time required to solvefor accurate azimuth, even though both antennas 26 a and 26 b may bemoving in space or not at a known location. The technique of resolvingthe attitude information and position information for the vehicle 10 mayemploy carrier phase DGNSS techniques with a moving reference station.Additionally, the use of data from auxiliary dynamic sensors aids thedevelopment of a heading solution by applying other constraints,including a rough indication of antenna orientation relative to theEarth's gravity field and/or alignment to the Earth's magnetic field.

Producing an accurate attitude from the use of two or more GNSS receiverand antenna systems 22 has been established in the art and thereforewill not be expounded upon herein. The processing is utilized herein aspart of the process required to implement an exemplary embodiment.

Referring also to FIG. 4, a mechanism for ensuring an accurateorientation of the sensor system 20 to the vehicle 10 may be providedfor by an optional mounting base 14 accurately attached to the enclosure28. An accurate installation ensures that substantially no misalignmenterror is present that may otherwise cause the sensor system 20 toprovide erroneous heading information. The mounting base 14 isconfigured such that it fits securely with a determinable orientationrelative to the vehicle 10. In an exemplary embodiment, for example, themounting base 14 is configured to fit flatly against the top surfaces ofthe vehicle 10 to facilitate an unimpeded view to the GNSS satellites.

With the sensor system 20 affixed and secured in the vehicle 10 power upand initialization of the sensor system 20 is thereafter executed. Suchan initialization may include, but not be limited to, using the controlsystem 100 to perform any initialization or configuration that may benecessary for a particular installation, including the configuration ofan internal log file within the memory of the sensor system 20.

The sensor system 20 may further include additional associatedelectronics and hardware. For example, the sensor system 20 may alsoinclude a power source 32, e.g., battery, or other power generationmeans, e.g., photovoltaic cells, and ultrahigh capacity capacitors andthe like. Moreover, the sensor system 20 may further include a controlsystem 100. The control system 100 may include, without limitation, acontroller/computer 102, a display 104 and an input device 106, such asa keypad or keyboard for operation of the control system 100. Thecontroller 102 may include, without limitation, a computer or processor,logic, memory, storage, registers, timing, interrupts, input/outputsignal interfaces, and communication interfaces as required to performthe processing and operations prescribed herein. The controllerpreferably receives inputs from various systems and sensor elements ofthe sensor system 20 (GNSS, inertial, etc.), and generates outputsignals to control the same and direct the vehicle 10. For example, thecontroller 102 may receive such inputs as the GNSS satellite andreceiver data and status, inertial system data, and the like fromvarious sensors. In an exemplary embodiment, the control system 100computes and outputs a cross-track and/or a direction error relating tothe current orientation, attitude, and velocity of the vehicle 10 aswell as computing a desired swath on the ground. The control system 100will also allow the operator to configure the various settings of thesensor system 20 and monitor GNSS signal reception and any other sensorsof the sensor system 20. In an exemplary embodiment, the sensor system20 is self-contained. The control system 100, electronics, receivers 24,antennas 26, and any other sensors, including an optional power source,are contained within the enclosure 12 to facilitate ease ofmanipulation, transportability, and operation.

Referring now to FIG. 5, a flowchart diagrammatically depicting anexemplary methodology for executing a control process 200 is provided.An exemplary control process 200, such as may be executed by an operatorin conjunction with a control system 100, acts upon information from thesensor system 20 to output cross-track and/or direction error based uponcorrected 3-D position, velocity, heading, tilt, heading rate (degreesper second), radius of curvature and the like.

System 22 a computes its position, denoted p1 (x1, y1, z1). Referringnow to block 220, the secondary receiver and antenna system 22 bcomputes its position, denoted p2 (x2, y2, z2). Referring now to block230, optionally additional receiver and antenna system(s) 22 computetheir respective positions, denoted p3 (x3, y3, z3), . . . pn (xn, yn,zn).

At process block 240, employing a geometric calculation the heading iscomputed as the vector perpendicular to the vector joining the twopositions, in the horizontal plane (assuming they are aligned with thevehicle 10). Furthermore, at block 250 the roll of the vehicle 10 mayreadily be computed as the arc-tangent of the ratio of the difference inheights of the two antennas 26 a and 26 b divided by the spacing betweentheir phase centers (a selected distance within the enclosure 12). Itwill be appreciated that optionally, if additional receiver and antennasystems are utilized and configured for additional measurements, thepitch and roll angles may also be computed using differentialpositioning similar to the manner for computing heading. Therefore, inFIG. 5, optionally at process block 260, the pitch and roll may becomputed.

Continuing with FIG. 5, at process block 270, using the computed rollangle and a known antenna height (based on the installation in a givenvehicle 10), the actual position at the center of the vehicle 10projected to the ground may be calculated. This position represents atrue ground position of the vehicle 10. Once the ground position isknown, the error value representing the difference between where thevehicle should be based on a computed swath or track, and where itactually is, can be readily calculated as shown at block 280.

Optionally, the vector velocities of the vehicle 10 are also known orreadily computed based on an existing course and heading of the vehicle10. These vector velocities may readily be utilized for control andinstrumentation tasks.

Turning now to FIG. 6, in another exemplary embodiment a steeringcontrol process 300 can utilize the abovementioned information from thesensor system 20 to direct the vehicle motion. At process block 310 thesteering control may be initiated by obtaining the computed errors fromprocess 200. Turning to block 320, the steering control process 300 maybe facilitated by computing a steering control command based on aproportionality factor times the difference in desired position versusactual position (computed position error), plus a second proportionalityfactor times the difference in desired heading versus actual heading(heading error). The second proportionality factor ensures that when thevehicle attains the desired position it is actually directed to thecorrect heading, rather than crossing the track. Such an approach willdramatically improve steering response and stability. At process block330, a steering command is generated and directed to the vehicle 10.

Moreover, continuing with FIG. 6, optionally a recursive adaptivealgorithm may also be employed to characterize the vehicle response andselected dynamic characteristics. In an exemplary embodiment, the sensorsystem 20 applies selected control values to the vehicle steeringcontrol mechanism as depicted at optional block 340 and block 330. Thesensor system 20 measures the response of the vehicle 10 as depicted atprocess block 350 and calculates the response times and characteristicsfor the vehicle. For example, a selected command is applied and theproportionality of the turn is measured given the selected change insteering. Turning to process block 360, the responses of the vehicle 10are then utilized to calibrate the control commands applying a modifiedcontrol command to achieve a desired response. It will be appreciatedthat such an auto-calibration feature would possibly be limited byconstraints of the vehicle to avoid excess stress or damage as depictedat 370.

It will be appreciated that while a particular series of steps orprocedures is described as part of the abovementioned alignment process,no order of steps should necessarily be inferred from the order ofpresentation. For example, the process 200 includes installation andpower up or initialization. It should be evident that power-up andinitialization could potentially be performed and executed in advancewithout impacting the methodology disclosed herein or the scope of theclaims.

It should further be appreciated that while an exemplary partitioningfunctionality has been provided, it should be apparent to one skilled inthe art that the partitioning could be different. For example, thecontrol of the primary receiver 24 a and the secondary receiver 24 b, aswell as the functions of the controller 102, could be integrated inother units. The processes for determining the alignment may, for easeof implementation, be integrated into a single receiver. Suchconfiguration variances should be considered equivalent and within thescope of the disclosure and claims herein.

The disclosed invention may be embodied in the form ofcomputer-implemented processes and apparatuses for practicing thoseprocesses. The present invention can also be embodied in the form ofcomputer program code containing instructions embodied in tangiblemedia, such as floppy diskettes, CD-ROMs, hard drives, or any othercomputer-readable storage medium 80 wherein the computer becomes anapparatus for practicing the invention when the computer program code isloaded into and executed by the computer. The present invention can alsobe embodied in the form of computer program code stored in a storagemedium or loaded into and/or executed by a computer, for example. Thepresent invention can also be embodied in the form of a data signal 82transmitted by a modulated or unmodulated carrier wave, over atransmission medium, such as electrical wiring or cabling, through fiberoptics or via electromagnetic radiation. When the computer program codeis loaded into and executed by a computer, the computer becomes anapparatus for practicing the invention. When implemented on ageneral-purpose microprocessor, the computer program code segmentsconfigure the microprocessor to create specific logic circuits.

III. Alternative Aspect GNSS Control Systems and Methods

FIG. 7A shows another alternative aspect of the invention including aGNSS antenna and gyroscope attitude system 402 with antennas 405, 406separated by a rigid link 407. In a typical application, the rigid link407 is attached to the vehicle 10 and extends along the X (transverse)axis or transversely with respect to the vehicle's direction of travel,which generally corresponds to the Y (heading) axis. Alternatively, thevehicle 10 itself can provide the rigid link between the antennas 405,406, for example, by mounting the antennas 405, 406 at predetermined,fixed locations on the roof of the vehicle cab with a predetermined,fixed distance therebetween. Another alternative is to provide a GNSSattitude device with antennas, receivers and sensors (e.g., gyroscopes(gyros), accelerometers and other sensors) in a self-contained, unitaryenclosure, such as the device 20 shown in enclosure 28 in FIG. 4.Regardless of the antenna-mounting structure, the orientation of theantenna pair and the rigid link 407 (or vehicle 10) is determined withrespect to an Earth-fixed coordinate system. The XYZ axes shown in FIG.7A provide an example for defining this relation. Roll and yaw gyros430, 440 are generally aligned with the Y and Z axes respectively fordetecting and measuring vehicle 10 attitude changes with respect tothese axes.

With the system 402 installed on a vehicle 10 (FIG. 8), the two antennas405, 406 can provide angular orientations with respect to two axes. Inthe example shown, angular orientation with respect to the Y (heading)axis corresponds to vehicle roll and with respect to the Z (vertical)axis corresponds to vehicle yaw. These orientations are commonly ofinterest in agricultural vehicles whereby this is the preferred mountingand orientation arrangement for such applications. The vehicle's rollmost adversely affects GNSS-measured vehicle cross-track error. Bymeasuring the vehicle's roll, such cross-track errors can be compensatedfor or eliminated. Such roll-induced cross-track errors include variableroll errors due to uneven terrain and constant roll errors due to hillslopes. It will be appreciated that adding a third antenna providesthree-axis (XYZ) attitude solutions corresponding to pitch, roll andyaw. Of course, reorienting the two-antenna system 402 can provide otherattitude solutions. For example, locating the antennas' baseline(aligned with the rigid link 407) fore-and-aft along the vehicle's Yaxis will provide pitch and yaw attitudes.

FIG. 7B shows the system 402 in a yaw attitude or condition whereby thevehicle 10 has deviated from a desired heading along the Y axis to anactual heading by a yaw angle θY. In other words, the vehicle 10 hasrotated (yawed) clockwise with respect to the Z axis. FIG. 7C shows thesystem 402 in a roll attitude or condition whereby the vehicle 10 hasdeviated from level to a tilt or roll angle of θR. In other words, thevehicle 10 has rotated (rolled) counterclockwise with respect to the Yaxis.

The system 402 includes roll and yaw gyros 430, 440 mounted and orientedfor detecting vehicle rotational movement with respect to the Y and Zaxes. The system 402 represents a typical strap-down implementation withthe vehicle 10, antennas 405, 406 and gyros 430, 440 rigidly connectedand moving together. A body-fixed coordinate system is thus defined withthe three perpendicular axes XYZ.

In all but the most extreme farmlands, the vehicle 10 would normallydeviate relatively little from level and horizontal, usually less than30° in most agricultural operations. This simplifies the process ofcalibrating the gyros 430, 440 using the GNSS attitude system 402consisting of two or more antennas 405, 406. For simplicity, it isassumed that the body-fixed axes XYZ remain relatively close to level.Thus, the change in the heading (yaw) angle θY of FIG. 7B isapproximately measured by the body-fixed yaw gyro 440, even though theremay be some small discrepancy between the axes of rotation. Similarassumptions can be made for the roll angle θR (FIG. 7C), which isapproximately measured by the body-fixed roll gyro 430. A similarassumption could be used for measuring pitch attitude or orientationangles with a pitch gyro.

This simplifying assumption allows the gyros to be decoupled from oneanother during integration and avoids the necessity of using a fullstrap-down quaternion implementation. For example, heading deviation isassigned only to the yaw gyro 440 (gyro axis perturbations from theassumed level axis alignment are ignored). Similarly, vehicle roll isassumed to be measured completely by a single roll gyro 430. GNSSattitude-measured heading and roll can then be used to calibrate thegyros 430, 440. Such simplifying assumptions tend to be relativelyeffective, particularly for agricultural operations on relatively flat,level terrain. Alternatively, a full six-degrees-of-freedom strap-downgyro implementation with quaternion integration could be employed, butsuch a solution would normally be excessive and represent an ineffectiveuse of computing resources, unless an inertial navigation system (INS)was also being used to backup GNSS, for example, in the event of GNSSsignal loss.

For the purpose of calibrating the gyroscopes 430, 440, the anglesmeasured by the GNSS attitude system 402 are used as truth in a Kalmanfilter estimator of gyro bias and scale factor errors. Over a smallinterval of time, T, the following equation holds:{dot over (θ)}_(gyro) T=Aθ _(true) +BTWhere{dot over (θ)}_(gyro)=average gyro reading over

$T = {{1/n}{\sum\limits_{n}{\overset{.}{\theta}}_{gyro}}}$(with n readings taken over time T)θ_(true)=truth angular change over interval T as measured by the GNSSattitude system.A=gyro scale factor errorB=gyro rate bias error

A two state Kalman filter is defined to have the gyro rate basis andscale factor error as states. The Kalman process model is a first-orderMarkov:

${X_{k + 1} = {{\begin{bmatrix}1 & 0 \\0 & 1\end{bmatrix}X_{k}} + {\begin{bmatrix}\sigma_{A} & 0 \\0 & \sigma_{B}\end{bmatrix}W_{k}}}}\mspace{14mu}$where  the  state  vector   X = [A  B]Here σ_(A) and σ_(B) are noise amplitudes and W is white noise. Thisdictates what is known as a random walk of the state [A B]. The designerof the Kalman filter chooses σ_(A) and σ_(B) according to how rapidlythe bias and scale factor errors are expected to vary (usuallyvariations due to temperature dependencies of scale and bias in a lowcost gyro). Typical variations, especially of the scale factor, arequite small (A and B are nearly constant), and σ_(A) and σ_(B) arechosen accordingly. Typical values for a low-cost gyroscope, using atime interval T are:

${\sigma_{A} = \frac{0.02T}{1200}},{\sigma_{B} = \frac{T}{1200}}$where T is expressed in seconds and 1200 means 1200 seconds. Forexample, here the random walk is chosen to cause a drift in scale factorof 0.02 in 1200 seconds.

The Kalman measurement equation is:y=Hx+vWherey={dot over (θ)}_(gyro), H=[θ_(true) T] and v is measurement noise. TheKalman covariance propagation and gain calculation is designed accordingto well-known techniques.

Similar Kalman filters are deployed in both yaw and roll (and/or pitch)channels. The GNSS attitude devices 20 provides a reference yaw and rollthat act as the Kalman measurements enabling the calibration of gyrorate basis and scale factor errors. The GNSS device provides heading androll, even when the vehicle is stationary or traveling in reverse. Thisprovides a significant advantage over single-antenna systems whichprovide a vehicle direction only when moving (i.e., a velocity vector).The multi-antenna attitude device 20 enables continuous calibrationregardless of whether or not and in what direction the vehicle 10 ismoving.

The calibrated gyros 430, 440 are highly advantageous in a vehiclesteering control system. High precision heading and heading-rateproduced by the calibrated yaw gyro is a very accurate and instantaneousfeedback to the control of vehicle changes in direction. The angularrate produced by the gyro is at least an order of magnitude moreaccurate than the angular rate produced by pure GNSS systems, even thosewith multiple antennas. The system 402 is also very responsive. Thefeedback control needs such relatively high accuracy and responsivenessin heading and heading-rate to maintain control loop stability. It iswell known that rate feedback in a control loop enhances stability. On afarm vehicle, where vehicle dynamics may not be fully known or modeled,this aspect is particularly important. The rate term allows a genericcontrol system to be developed which is fairly insensitive to un-modeledvehicle dynamics. A relatively accurate heading and heading-rate-of-turncan be calculated for use in a vehicle automatic steering system.

Another advantage of the system 402 is that a gyro calibrated to measuretilt angle can provide the vehicle's tilt much more accurately than asystem relying exclusively on GNSS positioning signals. This advantageis particularly important in high-precision autosteering, e.g., to thecentimeter level. Errors in GNSS attitude are effectively increased bythe ratio of the antenna spacing to the mounted height of the antennasabove the ground, as illustrated in FIG. 8, which shows an attitudesystem 402 comprising a pair of antennas 405, 406 connected by a link407, as described above. The system 402 is shown tilted through a tilt(roll) angle θ_(R). An imaginary antenna height line perpendicular tothe rigid link 407 is projected to the “true” ground position of thevehicle 10 in FIG. 8 and forms the roll angle with respect to the Zaxis. The relative antenna height differential can be projected alongthe vertical Z axis to a ground intercept point and establishes across-track error (distance between the vehicle true ground position andthe Z axis ground intercept point), whereby errors in the antenna heightdifferential are amplified by the ratio of the rigid link 407 length tothe antenna height. The spacing of the antennas 405, 406, whichcorresponds to the length of the rigid link 407, is typically limited bythe width of the vehicle 10, which can be relatively tall, therebyresulting in a relatively large antenna height-to-spacing ratio, e.g.,five-to-one. Furthermore, noise-induced errors present in GNSS relativeantenna height differentials (e.g., carrier phase noise, etc.) will bemultiplied by this ratio, which can cause steering errors, includingsteering oscillations, etc.

The GNSS attitude system 402 utilizes a roll gyro (e.g., 430) formeasuring rate-of-change of the roll angle, rather than the absoluteroll angle, which rate of change is integrated to compute absolute rollangle. The constant of integration can be initialized to the currentGNSS-derived roll angle and then subsequently steered to the GNSS rollangle by filtering with a Hatch filter or similar filter used forsmoothing the code phase against the carrier phase in the GNSSreceivers. Relatively smooth vehicle roll estimates can thus be achievedwith a gyro.

More specifically, in an exemplary embodiment, the filtering issupplemented by the equation:θ_(filter)(k)=Δ_(gyro)(k)+Gain*[θ_(GNSS)(k)−θ_(filter)(k−1)−Δ_(gyro)(k)]Δ_(gyro)(k)=θ_(gyro)(k)−θ_(gyro)(k−1)Where θ_(filter)(k) is the desired output roll angle (at time k)smoothed by gyro roll angle, but steered to GNSS roll angle. The GNSSroll (at time k) is θ_(GNSS) (k) while the raw gyro angular reading isθ_(gyro)(k) which is obtained by integrating gyro angular rate. Thedifference in gyro integrated rate over one time interval (k−1 to k) isdenoted Δ_(gyro)(k). The filter bandwidth and weighting of the GNSS rollangle into the solution is set by the filter's gain (denoted Gain). Onemethod to choose the gain is to assign Gain=T/τ where T is the time spanfrom epoch to epoch and τ is a time-constant, typically much larger thanT. The smaller the Gain, the less the GNSS roll angle is weighted intothe solution. The gain is chosen to give a smooth filtered roll output,dominated by the low gyro noise characteristics, but also maintainingalignment with GNSS roll. Since the gyro is calibrated in terms of itsscale and bias errors per the methods described earlier, the gain can bechosen to be very small (much less than 1) and still the filtered rollangle closely follows the GNSS roll angle, but without the noise of theGNSS derived roll angle. Similar schemes can be deployed for pitch andheading angles if needed, all with the benefit of improved steering ifsuch angles are used in the steering control feedback.

FIG. 9 shows a GNSS and gyroscopic control system 502 comprising analternative aspect of the present invention in a tractor and sprayeragricultural equipment application 504. The vehicle (e.g., a motivecomponent or tractor) 10 is connected to a working component (e.g., asprayer) 506 by an articulated connection 508, which can comprise aconventional tongue-and-hitch connection, or a powered, implementsteering system or hitch, such as those shown in U.S. Pat. No.6,865,465, No. 7,162,348 and No. 7,373,231, which are assigned to acommon assignee herewith and are incorporated herein by reference.

The tractor 10 and the sprayer 506 mount tractor and sprayer GNSSantenna and gyroscope attitude subsystems 510, 512 respectively, whichare similar to the system 402 described above and provide GNSS-derivedposition and attitude outputs, supplemented by gyro-derived rate ofrotation outputs for integration by the control system 502. The sprayer506 includes a spray boom 514 with multiple nozzles 516 providing spraypatterns 518 as shown, which effectively cover a swath 520. The system502 can be programmed for selectively controlling the nozzles 516. Forexample, a no-spray area 522 is shown in FIG. 9 and can comprise, forexample, an area previously sprayed or an area requiring spray. Based onthe location of the no-spray area 522 in relation to the spray boom 514,one or more of the nozzles 516 can be selectively turned on/off.Alternatively, selective controls can be provided for other equipment,such as agricultural planters wherein the seed boxes can be selectivelyturned on/off.

FIG. 10 shows some of the major components of the system 502, includingthe GNSS antenna and gyroscope attitude subsystems 510, 512 withantennas 405, 406 separated by rigid links 407, as described above, andinertial gyros 514. The tractor and implement 10, 506 can be equippedwith comparable systems including DGNSS receivers 524, suitablemicroprocessors 526 and the inertial gyros 529. Additional sensors 528can include wheel counters, wheel turn sensors, accelerometers, etc. Thesystem components can be interconnected by a CAN connection 530.Alternatively, components can be wirelessly interconnected, e.g., withRF transmitters and receivers.

In operation, the functions described above can be implemented with thesystem 502, which has the additional advantage of providing GNSS andgyro-derived positioning and attitude signals independently from thetractor 10 and the implement 506. Such signals can be integrated by oneor both of the microprocessors 526. The tractor 10 can be automaticallysteered accordingly whereby the implement 506 is maintained on course,with the additional feature of selective, automatic control of thenozzles 516. For example, FIG. 9 shows the course of the tractor 10slightly offset to the course of the sprayer 516, which condition couldbe caused by a downward left-to-right field slope. Such sloping fieldconditions generate roll attitudes, which could also be compensated foras described above. For example, the system 502 can adjust the outputfrom the spray nozzles 516 to compensate for such variable operatingconditions as sloping terrain, turning rates, tire slippage, systemresponsiveness and field irregularities whereby the material isuniformly applied to the entire surface area of the field. Moreover, theGNSS-derived positioning and heading information can be compared toactual positioning and heading information derived from other sensors,including gyros, for further calibration.

IV. Multi-Antenna High Dynamic Roll Compensation and Rover L1 RTK

Another alternative aspect GNSS guidance system 602 is shown in FIGS. 11and 12 and provides high dynamic roll compensation, heading andrate-of-turn (ROT) in an RTK system including a GNSS receiver 604including an RF converter 606 connected to a multi-channel trackingdevice 608 and first and second antennas 610, 612, which can be mountedon top of a vehicle 10 in fixed relation defining a transverse (X axis)fixed baseline 614. The receiver 604 provides a GNSS data output to aguidance processor (CPU) 616, which includes a GUI/display 618, amicroprocessor 620 and media (e.g., for data storage) 622. A steeringvalve block 624 includes autosteer logic 626, hydraulic valves 628 andsteering linkage 630. A wheel sensor 632 is connected to the steeringvalve block 624, which in turn is connected to the guidance processor616 by a suitable CAN bus 634.

GNSS positioning signals are received from a constellation of GNSSsatellites and an RTK base transceiver 636, which includes a receiver638 and a transmitter 640 for transmitting carrier phase signals to arover RTK receiver 642. By using GNSS positioning signals from thesatellites and correctional signals from the RTK base transceiver 636,the guidance system 602 can calculate a relatively accurate positionrelative to the base transceiver 636, which can be located at apredetermined position, such as a benchmark. The guidance system 602described thus far is an RTK system utilizing a dual frequency receiverand is capable of achieving sub-centimeter accuracy using the carrierphase signals.

Roll compensation, heading and rate of turn can all be calculated usingvector-based heading (yaw and roll) information derived from the roverGNSS receiver 604. High-dynamic vehicle roll is a problem with certainapplications, such as agricultural vehicles, which traverse uneventerrain and tend to be relatively tall with antennas mounted threemeters or more above ground level. Antenna arrays can swing significantdistances from side to side with vehicle roll, as indicated by a rollarrow 644. Such deviations can be detrimental to precision farming, andrequire compensation. The fixed-baseline vehicle antennas 610, 612provide the necessary dynamic vector outputs for processing andcompensation by the steering valve block 624. For example, themicroprocessor 620 can be preprogrammed to instantly respond to suchroll errors by providing counteracting output signals via the CAN bus634 to autosteer logic 626, which controls the hydraulic valves 628 ofthe steering valve block 624. A slight delay phase shift can beprogrammed into the microprocessor 620, thus reflecting the inherent lagbetween vehicle roll and the steering system reaction. The delay phaseshift can be adjustable and calibrated for accommodating differentequipment configurations. The GNSS receiver 604 output providesrelatively accurate guidance at slow speeds, through turns and inreverse without relying on sensing vehicle motion via an inertialnavigation system (INS), utilizing gyroscopes and/or accelerometers.Moreover, the guidance system 602 can eliminate the calibrationprocedures normally needed for INS-corrected systems.

The system 602 can likewise provide high dynamic yaw compensation foroscillation about the vertical Z axis using the two-antenna fixedbaseline configuration of the receiver 604. Adding a third antenna wouldenable high dynamic compensation with respect to all three axes XYZe.g., in a six-degrees-of-freedom mode of operation.

Providing multiple antennas 610, 612 on a rover vehicle 10 cansignificantly improve the ability to resolve integer ambiguities byfirst obtaining an attitude solution by solving for the locations of therover antennas 610, 612 with respect each other. Then, using thenon-relative locations and the known relative ambiguities, solving forthe global ambiguities using observations taken at each antenna 610,612. The number of observations is thus significantly increased overconventional RTK. Solving the global ambiguities enables locating therover antennas 610, 612 in a global sense relative to a base station636. Using multiple antennas in this manner enables using L1 singlefrequency receivers, which tend to be less expensive than dual frequency(L1 and L2) receivers, as in conventional RTK systems. An exemplarymethod consists of:

-   -   1. Transmitting code and carrier phase data from a base station        636 to a multiple antenna rover system (e.g., 602).    -   2. At the rover 602 side, determining the relative locations and        the relative ambiguities of the multiple antennas using an        attitude solution taking advantage of known geometry constraints        and/or a common clock. Such a method is disclosed in U.S. Pat.        No. 7,388,539, which is assigned to a common assignee herewith        and is incorporated herein by reference.    -   3. Optionally store off the attitude solution (locations and        ambiguities) for later time-tag matching with the data from the        base station 636. Optionally, also store off the current GNSS        observations (carrier phase) for the same purpose. Although this        step is not necessary, time tag matching of base and rover data        improves results by avoiding extrapolation errors.    -   4. Form single or double difference equations and solve for the        global ambiguities using knowledge of the relative antenna        locations and/or common clocks and/or the relative ambiguities.

Example using a two-antenna rover system (e.g., 602):

-   -   At antenna 1 (e.g., 610) of the rover, we can write the equation        R1=[A]x1−N1,    -   where R1 is a carrier phase observation vector (single or double        difference) at antenna 1, A is a design matrix, X1 is the        location vector of antenna 1 (may include clock if single        differencing is used), and N1 is an ambiguity vector for antenna        1.    -   Similarly, at antenna 2 (e.g., 612) we can write        R2=[A]x2−N2    -   Where R2 is a carrier phase observation vector at antenna 1, A        is a design matrix, X2 is the location vector of antenna 2, and        N2 is an ambiguity vector for antenna 2.    -   Note, that in this example, the design matrix A is taken to be        the same in both antenna equations. But, this is true only if        both antennas see the same satellites. A more general example        would use separate A1 and A2 for the two equations.    -   Solving an attitude solution (for example, see U.S. Pat. No.        7,388,539), we find the relative antenna displacement V, and the        relative ambiguity M where        V=x2−x1        and        M=N2−N1        Thus, combining the above equations, we have        R1=[A]x1−N1        R2=[A](x1+V)−(N1+M)        Rearranging gives        R1=[A]x1−N1        R2−[A]V+M=[A]x1−N1        And, combining into a single vector equations gives        R=[A]x1−N        Where        R=[R1,R2−[A]V+M]^(T) and N=[N1,N1]^(T)    -   Where ‘T’ denotes transpose        Referring to the above example, twice as many equations are        obtained for the same number of unknowns (e.g. X1 and N1).        Solving for the global integer ambiguity N1 is facilitated by        the multiple available equations.

Multiple antennas can also be utilized at the base and would provide theadvantage of canceling multipath signals. However, multiple antennas onthe rover are generally preferred because they provide attitude for therover 10, which is generally not of concern for the base 636.

V. Moving Baseline Vehicle/Implement Guidance Systems

Alternative embodiment multiple-antenna GNSS guidance systems are shownin FIGS. 13-18 and utilize a moving baseline between a vehicle-mountedantenna(s) and an implement-mounted antenna. Independent implementsteering can be accomplished with a powered, implement steering systemor hitch, such as those shown in U.S. Pat. No. 6,865,465, No. 7,162,348and No. 7,373,231, which are assigned to a common assignee herewith andare incorporated herein by reference.

FIGS. 13-14 show a GNSS guidance system 726 comprising another modifiedembodiment of the present invention and including a vehicle 10 connectedto an implement 728 by a hitch 730. The hitch 730 permits the implement728 to move through three axes of movement relative to the vehicle 10 asthe system 726 maneuvers and traverses ground with irregularitiescausing the vehicle 10 and the implement 728 to yaw, pitch and rollsomewhat independently of each other. A moving baseline 732 is definedbetween points on each, e.g., between a vehicle antenna 753 and animplement antenna 756. The moving baseline 732 is generally a 3D vectorwith variable length and direction, which can be derived from thedifferences between the vehicle antenna 753 location (X1, Y1, Z1) andthe implement antenna location (X3, Y3, Z3), or other predeterminedpoint locations on the vehicle 10 and the implement 728. The guidancesystem 726 includes a single GNSS receiver 734 (e.g., a single printedcircuit board (PCB) receiver) receiving ranging data streams from theantennas 753, 756, which can include the normal front end RFdownconverter components. Using the geodetic-defined position solutionsfor the antennas 753, 756, the moving baseline 732 is defined and usedby a guidance CPU 736 in real-time for computing guidance solutions,which include steering command outputs to the steering valve block 738.The varying separation of the antennas 753, 756 occurs both at the startof attitude acquisition and during operation.

FIG. 15 shows another alternative aspect vehicle/implement GNSS guidancesystem 740 with first and second vehicle antennas 753, 754, which caninclude front end down converter RF components providing ranging signaloutputs, along with the implement antenna 756, to the single GNSSreceiver 734 as described above. The vehicle antennas 753, 754 define afixed baseline 754 by their respective positions (X1, Y1, Z1), (X2, Y2,Z2), which function to provide vector heading and rate-of-turn (ROT)output information. Such positioning data is input to the guidance CPU736 by measuring yaw and roll attitudes whereby such guidance andperformance information can be determined solely on GNSS-defined rangingdata utilizing the fixed-relationship mounting of the vehicle antennas753, 754 on the vehicle 10. Such information can be processed inconnection with the implement antenna 756 position information in orderto provide more complete GNSS positioning and guidance solutions,including travel paths for the vehicle 10 and the implement 728.

FIG. 16 shows another modified aspect GNSS positioning system 752, whichincludes first and second vehicle antennas 753, 754 at GNSS-definedpositions (X1, Y1, Z1), (X2, Y2, Z2) respectively, which positionsdefine a vehicle fixed baseline 755. The implement 728 includes firstand second implement antennas 756, 757 at GNSS-defined positions (X3,Y3, Z3), (X4, Y4, Z4) respectively, which define an implement fixedbaseline 758 and from which the guidance CPU 736 determines heading andROT for the implement 728 using similar vector techniques to thosedescribed above. A movable baseline 759 can be defined between a vehicleantenna 753 and an implement antenna 756 as shown, or between othercorresponding antenna pairs, or other predetermined locations on thevehicle 10 and the implement 728. The system 752 utilizes a single GNSSreceiver 734 receiving input ranging information from the four antennas753, 754, 756, 757 and providing a single output stream to the guidanceCPU 736. It will be appreciated that various other antenna/receivercombinations can be utilized. For example, a third vehicle and/orimplement antenna can be provided for 3-axis attitude computation. INScomponents, such as gyroscopes and/or accelerometers, can also beutilized for additional guidance correction, although the systemsdescribed above can provide highly accurate guidance without such INScomponents, which have certain disadvantages.

FIG. 17 shows the 2+1 antenna system 740 operating in a guidance modewhereby a predetermined number of positions 790 at predeterminedintervals are retained by the guidance CPU 736, thereby defining amulti-position “breadcrumb” tail 792 defining the most recent guidepathsegment traversed by the vehicle 10 based on the locations of thevehicle antenna(s) 753 (754). Although the 2+1 antenna guidance system740 is used as an example, the 1+1 antenna guidance system 726 and the2+2 guidance system 752 can also be used in this mode and function in asimilar manner, with more or less ranging signal sources. The guidanceCPU 736 utilizes the retained tail “breadcrumb” positions 790 inconjunction with the GNSS-derived antenna locations for computing acrosstrack error representing implement 728 deviation from a desiredguidepath 794, and the necessary steering signals for correcting thevehicle 10 course to maintain the implement 728 on track. Still further,in a multi-position tail 792 operating mode the high dynamic rollcompensation function described above can be utilized to compensate forvehicle and/or implement roll using the fixed baseline(s) 746, 755, 758for further guidance solution accuracy based solely on GNSS ranginginformation.

With the systems 726, 740 and 752, a single receiver can be used forachieving carrier phase relative accuracy, even without differentialcorrection. A single clock associated with the receiver facilitatesambiguity resolution, as compared to dual receiver and dual clocksystems. Direct connections among the components further enhanceaccuracy and facilitate high dynamic roll corrections, as describedabove. Continuous base and rover ranging data are available forpositioning and control. With the 2+1 and the 2+2 configurations, thefixed baseline(s) provide heading and ROT guidance for the vehicleand/or the implement. Steering control for the vehicle is derived fromcrosstrack error computations utilizing the multiposition tail 792.

FIG. 18 is a schematic block diagram showing the components of the GNSSguidance systems 726, 740 and 752. The vehicle 10 components include aGNSS receiver 734 including a first vehicle antenna 753, an optionalsecond vehicle antenna 754, an RF down converter 764, a tracking device766 and an optional rover RTK receiver 768. A guidance processor CPU 736includes a GUI display 772, a microprocessor 774 and a media storagedevice 776. Vehicle steering 778 is connected to the guidance processorCPU 736 and receives steering commands therefrom. GNSS-derived data istransferred from the GNSS receiver 734 to the guidance processor CPU736. The implement 728 mounts an implement positioning system 780including a first implement antenna 756 and an optional second implementantenna 757, which are connected to the vehicle GNSS receiver 734 andprovide GNSS data thereto. An implement steering subsystem 784 receivessteering commands from the guidance processor CPU 736 via a CAN bus 786.The implement 728 is mechanically connected to the vehicle 10 by a hitch788, which can be power-driven for active implement positioning inresponse to implement steering commands, or a conventional mechanicallinkage. The hitch 788 can be provided with sensors for determiningrelative attitudes and orientations between the vehicle 10 and theimplement 728.

VI. Multi-Vehicle GNSS Tracking Method

FIG. 19 shows a multi-vehicle GNSS tracking system 802 adapted fortracking primary and secondary rover vehicles 804, 806, which cancomprise, for example, a combine and an offloading truck. Otherexemplary multi-vehicle combinations include crop picking and harvestingequipment, snowplows, aircraft engaged in mid-air refueling, etc. Datatransfer among the vehicles 804, 806 and a base transceiver 808 can beaccomplished with short-range radio links, such as Bluetooth and Wi-Fiwireless technologies. For example, the base transceiver 808 cantransmit corrections to the rovers 804, 806 at predetermined intervalsof one second (i.e., 1 Hz).

Between the base transmissions the primary rover 804 can transmit itsidentifying information (ID) and GNSS-derived position and timinginformation to the secondary rover 806. The secondary rover 806 thusreceives both differential corrections and the primary rover data overthe same radio link, or through an additional radio link. Such data cancomprise a multi-position tail 810 as described above and against whichthe secondary rover 806 can guide. For example, the secondary rover 806can directly follow the primary rover 804 at a predetermined distance byaligning its travel path with the multi-position tail 810 at apredetermined following distance, or it can offset its own paralleltravel path a predetermined offset distance, as shown in FIG. 19. Thesecondary rover 806 can position itself relative to the primary rover804 based on either a predetermined time interval or a predeterminedseparation distance. As discussed above, the multi-position tail 810 canautomatically update whereby only a predetermined number of detectedpositions are stored, which can correspond to a predetermined timeduration or distance behind the primary rover 804.

FIG. 20 shows a schematic block diagram of components comprising themulti-vehicle tracking system 802. The onboard systems for the primaryrover 804 and the secondary rover 806 can be similar to thevehicle-based GNSS guidance systems described above, with the additionof an inter-rover radio link 812.

VII. Earth-Moving Machine Control System 1002

In another alternative embodiment, a multi-antenna GNSS positioning andguidance control system 1003 is combined with various sensors on a pieceof excavation equipment 1004 to form a GNSS positioning and guidanceexcavation system 1002. Without limitation on the generality of usefulapplications of the system 1003, an excavator 1004 is shown as anexample of earth-moving equipment which can benefit from the presentinvention. Other suitable earth-moving examples include, withoutlimitation, backhoes, loaders, bulldozers, trenching machines and road(motor) graders.

Using GNSS positioning and guidance control can improve accuracy overmanual control in typical earth-moving tasks. The positioning andguidance system 1002 can be geo-referenced based on a digital terrainmap established prior to working a piece of land. Positioning inrelation to a predetermined geodesic reference system is generally basedon “absolute” coordinates, which can be determined using GNSS-basedranging measurements. Alternatively, “relative” positioning can be basedon a site-specific benchmark position set by positioning the bucket 1010of an excavator 1004 at a stake 1024 (FIG. 23) and programming a desiredelevation level based on the X, Y and Z coordinates of the stake.Further operations are based on absolute GNSS-defined coordinates in thegeo-referenced operating mode, or relative coordinates in themachine-referenced mode. Of course, the relative coordinates can beconverted to absolute coordinates using, for example, an absoluteposition of a benchmark or monument reference point.

FIG. 21 shows the excavator 1004 equipped with an articulated armcomprised of a hingedly connected boom 1006, a stick 1008 and a bucket1010. FIG. 21 demonstrates the six possible directions of movement theGNSS system can detect, including roll, pitch and slew (comparable toyaw) rotation about the X, Y, and Z axes respectively. The system 1002can be programmed for XYZ axial orientations in various combinations anddirections with respect to the equipment 1004, of which the XYZrotational axes orientation shown in FIG. 21 is one example. Threeantennas 1012 a,b,c are located on the body of the excavator 1004 for 3Dattitude determinations by comparing the GNSS-defined locations of theantennas 1012 a,b,c relative to each other. Three or more antennas 1012enable measuring movements in the six possible directions mentionedabove using GNSS ranging measurements. Inertial gyro and accelerometersensors can supplement the GNSS signals, or provide position andattitude solutions with one or two antennas.

FIG. 22 shows the excavator 1004 with various sensors and a GNSS-basedmachine control system 1003. The system 1003 is comprised of typicalGNSS elements, such as three antennas 1012, a GNSS receiver 1014, aguidance CPU 1016 which is capable of calculating positional datareceived by the receiver along with other necessary computations, and astorage device 1018 contained within the guidance CPU 1016 for storingposition data, pre-created terrain maps, and other necessary data. Thecontrol CPU is connected to a graphical user interface (GUI) 1017located within the cab. A base GNSS receiver and transmitter(transceiver) 1030 can be located at a predetermined, known location foroperating in a differential GNSS (DGNSS) mode, which can significantlyimprove positioning accuracy. The control system 1003 can also beconfigured for and operate in a real-time kinematic (RTK) mode. Amultiple-antenna (base and rover) system and method for vehicle guidanceand machine control are shown in co-pending U.S. patent application Ser.No. 12/857,298, which is assigned to a common assignee herewith and isincorporated herein by reference. Without limitation on the generalityof useful antenna and receiver configurations, the A220 and A320 (rover)and A221 (base) “smart” antennas and the Crescent® (single frequency)and Eclipse™ (dual frequency) receivers available from AgJunction LLC ofHiawatha, Kans. are suitable for use in the control system 1003.

The excavator 1004 further includes an implement arm 1005 comprised of aboom 1006, a stick 1008 and a bucket 1010, each of which includes arespective articulation sensor 1007, 1009, 1011. Each of thearticulation sensors measures the absolute angle of itself (i.e., boom1006, a stick 1008 and a bucket 1010) relative to the plane of itsorientation/installation (assuming single axis sensor) and thegravitational vector. The output signals from the articulation sensors1007, 1009, 1011 are processed and combined in the control CPU 1016 withother orientation information, such as the output from other machineangle sensors, the GNSS receiver 1014 and the IMU 1015 for computing acomplex position/orientation/attitude solution for the excavator 1004,including solutions for its individual articulated components ofinterest, in relation to a specific grading plan, GIS database or otherproject information source. For example, the bucket 1010 can bepivotable on multiple axes for greater control and flexibility, withsuch pivoting movements actuating additional sensors for monitoring andcontrolling the 3-D position and attitude of the bucket 1010. Stillfurther, additional GNSS antennas can be located on components of theimplement arm 1005 for locational data, either absolute or in referenceto the equipment 1004.

The guidance CPU 1016 determines the Z coordinate of the excavator 1004using the onboard GNSS positioning system. Because there are at leastthree antennas 1012 a,b,c located on the excavator 1004, the guidanceCPU 1016 also detects the instantaneous pitch, roll and slew of theexcavator 1004. The sensors 1007, 1009, 1011 located on the articulatedarm 1005 are electrically connected to the guidance CPU 1016 and providethe additional data necessary for the guidance CPU 1016 to determine theposition (including elevation) and attitude of the bucket 1010.Additional sensors can be employed for determining other equipmentrelationships, such as bucket 1010 orientation with respect to 3 axesfor buckets and other articulated tools movable with respect to multipleaxes. This is necessary because the bucket 1010 performs the digging andmeasuring functions necessary to determine whether the task of cuttingor filling is complete. By placing the bucket 1010 on grade or beneaththe ground level, the guidance CPU 1016 can determine whether thedesired ground-level elevation has been reached.

FIG. 23 shows a cross-sectional view of an excavator 1004 located on asloped piece of land. The current existing or original ground line 1028denotes where the soil surface exists prior to performing earth-movingtasks. FIG. 23 also shows a cut zone 1020 and a fill zone 1022. Thesezones are determined based on the desired design elevation line 1026.This design elevation line 1026 can be predetermined prior to performingexcavation on the site. A design elevation 1026 can be chosen for anumber of reasons, such as drainage or soil type. Soil above this designelevation 1026 is designated as a cut zone 1020, and the volume locatedbelow the design elevation 1026 is designated as a fill zone 1022.

The design elevation 1026 can be established in a number of differentways. First, the design elevation 1026 may be set by creating a terrainmap prior to performing any work on the site. This terrain map can be athree dimensional guidance map that is stored in the GNSS storage device1018 connected to the guidance CPU 1016. The terrain map contains thedesired elevations (Z coordinates) for a particular site, where the siteis defined by the X and Y coordinates in a horizontal plane. The GNSSguidance system will then guide the excavator 1004 around the site,designating what areas need to be cut or filled, depending on the designelevation 1026.

Alternatively, the relative design elevation 1026 can be defined inrelative terms based on a benchmark such as a stake 1024 placedsomewhere on the site at the desired design elevation 1026. If theentire site must be cut, the guidance CPU 1016 can take this intoaccount and define the design elevation 1026 at an elevation below thestake 1024. A similar correction can be applied if the entire site is tobe filled.

FIGS. 24A & 24B show a flowchart demonstrating steps for performing amethod of the present invention. The process starts at 1050. The chosensite is prepared at 1052 by removing brush, trees and otherobstructions. A grading plan is established at 1054 to determine thedesired design elevation, finished grade slope, and other optionsnecessary for proper drainage and structural support from the soil.

A choice is made at decision box 1056 whether to proceed using a digitalterrain map. As described briefly above, the digital terrain map is amap of the chosen site in three dimensions (3D). The design elevation isapplied to the map so that a pre-planned cut and fill plan is created.The terrain map establishes a benchmark based on a pre-planned andpreprogrammed map. The terrain map is stored in the guidance CPU'sstorage device 1018 at 1072.

The guidance system is then initialized at 1060, and the system guidesthe excavator 1004 throughout the site's various cut and fill zones1020, 1022. The system 1002 geo-references the benchmark designelevation 1026 at 1064 (“Bench In”) by referencing actual GNSS positionswith the pre-planned terrain map. Cut and fill operations are initiatedat 1066. Once a cut or fill has been made, the system compares the GNSSpositional data of the bucket within the cut or filled zone with thedesired design elevation denoted by the terrain map at 1074. A check isthen performed at 1070 to determine whether a design elevation has beenreached, which can be designated by a software-defined “dead zone”corresponding to the working tool (e.g., bucket 1010) being locatedwithin final design tolerances. If a design elevation 1026 has beenreached (positive branch from decision box 1070), Phase One is complete,and Phase Two begins. If not (negative branch from decision box 1070),additional cuts and fills are performed until a design elevation 1026 ismet. The GUI 1017 can indicate current positions in relation to finaldesign elevations, thus providing the operator with a visual indicationof task progress.

If a terrain map is not used (negative branch from decision box 1056),the next step is placing an elevation stake or stakes in the desiredsite at 1058. These stakes are used to set a benchmark or monumentdesign elevation 1026. Stakes are placed at locations of known elevationthroughout the field, or at one known location, and are referred to asbenchmarks or monuments. The process is then initialized at 1060. Thebucket is placed on top of the initial stake at 1062 (“Bench In”), theGNSS system 1003 detects and computes the 3-D position of the bucket andgeo-references that as the benchmark or monument at 1064. The excavatorthen begins to cut and/or fill the site at 1066. After a cut or fillaction is performed, the GNSS position of the bucket 1010 is checked at1068, and a check against the design elevation is made at 1070, e.g., ifthe bucket is within the predefined design tolerance dead zone. Theposition of the bucket 1010 relative to the design elevation 1026 can bedisplayed to the operator via the GUI 1017, e.g., as a graphical gradingdepiction showing existing and final grade elevation lines and cut andfill zones similar to those shown in FIG. 23. If the design elevation1026 has been reached, the process proceeds to Phase Two. If the designelevation 1026 has not yet been reached, the method returns to cutand/or fill the rest of the site at 1066 until the design elevation isreached.

FIG. 24B contains Phase Two, which is a continuation of Phase Onecontained on FIG. 24B. The first step in Phase Two is to determinewhether or not a slope check is desired at 1076. If yes, the bucket isplaced at GNSS point ‘A’ at 1078, and then at GNSS point ‘B’ at 1080.The bucket marks these two points and they are stored into the storagedevice. The guidance CPU 1016 then calculates the slope at 1082 usingthe “rise divided by run” formula:

${Slope} = \frac{Z_{A} - Z_{B}}{{XY}_{A} - {XY}_{B}}$

Once the slope check is performed at 1082, or alternatively if no slopecheck is desired at 1076, the results are displayed on the GUI 1017 at1084. The GUI 1017 may be a computer display connected to the GNSSsystem wirelessly, or a wired display within the cab of the excavator,or any other feasible means of connecting a display to the GNSS guidancesystem.

The guidance CPU then computes the volume of material (V_(m)) that hasbeen cut or filled at 1086. This is calculated by the guidance system1003 depending on the starting elevation as detected by the GNSSguidance system or as shown on the terrain map initially, and the knowndesign elevation obtained when work is complete. The V_(m) is thenstored at 1088, reported at 1090, and credited at 1092. The method endsat 1094. The system 1002 is adapted for interfacing with various projectcost accounting and related functions. For example, work reportscorresponding to material volumes (V_(m)) can be regularly (e.g., daily)generated for billing purposes. Productivity computations, machinescheduling and other support data processing operations can be performedremotely using data downloaded from the system 1002. For example, acentralized control operation can receive and process data from multiplesystems 1002, e.g., a fleet of excavators 1004 and other equipmentengaged on one or more projects. Specific assignments can be delegatedto the individual equipment units based on equipment capabilities,scheduling and other variables associated with project tasks.Alternatively, “smart” excavators equipped with the system 1002 can beprogrammed for accomplishing such tasks on board or in a networked groupof computers distributed throughout a fleet of machines. Examples ofsuch automation, collaboration and task decomposition relating toautomated machine behavior are disclosed in co-pending andcommonly-assigned U.S. Patent Applications No. 61/243,417; No.61/243,475; No. 61/265,281; and Ser. No. 12/760,363, which areincorporated herein by reference. Still further, machine usage,productivity and profitability can be determined, analyzed and reported.Equipment maintenance and machine assignments corresponding to specificprojects can also be facilitated using the data obtained via the system1002.

A repetitive, progressive pattern of motion or “macro” can be programmedto control the machine 1004 through multiple repetitive steps until adesired result, e.g., a grading plan, is achieved. For example, digginga trench typically involves removing earth from the same area anddepositing it in a predetermined area with each scoop. FIGS. 24C and 24Dshow a flowchart demonstrating steps necessary to perform a task usingmacros. The process starts at 1100. Operation of the macro can beactivated by operator command 1104 or by an “auto-engage” criteria 1102,such as commencing an earth-moving job involving repetitive machinemotions in the same general area. The system 1003 can be preprogrammedwith manual entry 1106 of either general or job-specific macros.Alternatively, the operator can create a custom macro by recording at1108 the actions he or she takes with the machine 1004 for automatedrepetition.

The macro can repeat the machine operation exactly at 1110 and controlthe machine 1004 through identical, repetitive motions, or incrementmachine operation at 1112 and incrementally change each motion to, forexample, remove earth from slightly lower depths on each scoop until a“dead band” signal corresponding to a final design elevation isachieved. For example, in controlling a backhoe digging a trench, eachscoop would be slightly deeper and/or horizontally repositioned.

Still further, the macro could be “geo-referenced” at 1114 for repeatingthe same action in the same location, independent of the equipmentpositioning. Geo-referencing could occur at a particular locationdefined in 3 dimensions, or along a 3-dimensional courseway, such as aroadway, trench, waterway, utility line right-of-way, etc. Controllingthe delta (i.e., differential A) corresponding to incremental machineoperation changes could control the rate of progress of the job.Progress along a work path can be defined and adjusted by the operatoror the macro programmer whereby predetermined increments of earth-movingoccur with each repetitive machine cycle of movement (e.g.,“cut-and-dump”).

An operator can alter only a subsection of the macro, allowingsubsequent machine cycles to resume an original preprogrammed movement.For example, a road grader might operate along a predeterminedgeo-referenced path in a particular manner subject to a “delta” variablecontrolled by the operator, whereafter predetermined macro control couldresume. Alternatively, operations could be machine-referenced at 1116rather than geo-referenced. Still further, such macro operation can beadapted for various work areas, including “courses” as discussed above,or entire field areas in agricultural operations.

Still further, macro control can be “open-ended” with distinct start andend states corresponding to a finite job 1118, or an endless repetitive“loop” continuing indefinitely until the operation is terminated by anoperator interrupt at 1126. After the macro has been assigned, the task1120 is performed. If the macro is a finite job, the task is eithercomplete at 1122 or incremented at 1124. If the macro is a loop, thetask 1120 is performed continuously until there is an operator interruptat 1126.

The operator could alter the machine movement during that portion of themacro (“delta control”), and then release manual control of theoperation for continuation with the original macro control. Such “delta”control could be one-time or recorded by the controller 1016 forrepetition. The operator on a trenching job, for example, could merelyreposition the equipment, while allowing automatic material extractionand dumping functions under computer control using such a macro. Theprocess ends at 1128.

FIG. 25 shows a road (motor) grader 1204 equipped with a GNSS guidancesystem 1202 comprising another alternative embodiment of the presentinvention. Like the excavator 1004 discussed above, three antennas 1212a,b,c are placed on the body of the grader 1204 and connected to a GNSSreceiver 1214, which connects to a CPU 1216 containing a storage device1218. The grader 1204 includes a grader blade 1206 mounting bladeantennas 1213 a,b. The grader blade 1206 can be raised, lowered andtilted by a pair of actuators 1208 connected to the body of the grader1204 and controlled by the system 1202.

The grader blade 1206 is adapted for vertical Z-axis movement and yawrotation about the Z-axis. The blade 1206 can also be tilted by rotatingit about a generally transverse Y axis, and can be adapted forpositioning through six degrees of freedom. Thus, in performing guidancetasks similar to the excavator mentioned above, the guidance system CPU1216 is adapted for controlling optimal positioning of the guidanceblade 1206, guiding the grader 1204 and performing all necessary machinecontrol and guidance functions for a predetermined task, such as gradinga road, a paved area or other structure. Alternatively, relativepositioning sensors, such as those described above, could be providedfor the blade 1206.

VIII. Additional Alternative Embodiments for Snow Grooming MachineControl and Guidance Applications

FIGS. 26-35 show a system 1302 and method adapted for guidance andmachine control in connection with, for example, snowcats, snowmobilesand other vehicles and mobile equipment used for grooming ski runs andtrails, and for similar operations. The system 1302 generally includesan equipment control subsystem 1304 adapted for mounting in a mobilepiece of equipment 1306, such as the snow grooming equipment, e.g. andwithout limitation, a snowcat as shown in FIG. 27, an RTK base unit 1308and an interconnected facility, such as a “back office” 1310. Althoughsnow grooming equipment 1306 is shown and described, other types ofmobile equipment can be utilized with variations of the system 1302,such as the construction and maintenance equipment described above. Theequipment control subsystem 1304 generally includes a GNSS receiver1312, a vehicle-mounted antenna 1313, an RF converter 1314, a trackingdevice 1316 and a rover RTK receiver 1318, which is adapted to receivedifferential GNSS signals from the base unit 1308. Various suitable GNSSreceivers can be used in the system 1302.

A guidance/machine control computer 1320 includes a microprocessor 1322and a graphic user interface (GUI)/display 1324. Data from the receiver1312 is communicated to the computer 1320 via a data connection or link1326. Other inputs to the computer 1320 include vehicle sensors 1328,inertial measurement units (IMUs) 1330 and an optional transceiver 1332,which can interconnect with the back-office 1310 or a network, such asthe Internet/WAN/LAN, generally depicted as a cloud 1334 andinteractively connected to the equipment control subsystem 1304 via adata link 1336. The mobile equipment 1306 can include snow groomingequipment 1338, such as the snowplow 1340 and the packing roller 1342shown in FIG. 27. The snowplow 1340 can mount a pair of antennas 1339for GNSS (e.g., RTK) based positioning and machine control inconjunction with positioning sensors mounted on the snowcat 1306. Thesnow grooming equipment 1338 can operate similarly to the earth workingand grading equipment described above, including the use of GNSS formachine control and guidance. Positioning and operation of the snowplow1340, the packing roller 1342 and other equipment can be independentlycontrolled via the guidance/machine control computer 1320, which can beprogrammed for coordinating such control and guidance with the mobileequipment 1306.

A power coupling 1344 provides power to the grooming equipment 1338 fromthe vehicle/equipment 1306. The power coupling 1344 can be mechanical,hydraulic, pneumatic, electrical, etc. For example, piston and cylinderunits 1346 are shown in FIG. 27 for operating and variably positioningthe snowplow 1340.

The remote facility or back-office 1310 connects to the cloud 1334 by adata connection 1348, which can comprise a Wi-Fi connection or someother suitable wireless interconnection, such as a Bluetooth, Android orother device. Other data transfer devices and protocols can be used fortransferring data from the mobile equipment 1306 to the remote facility1310. The remote facility 1310 can include suitable components, such asan input device 1352, a computer 1354 and an output device 1356. Datareceived in the remote facility 1310 can be processed and utilized forbusiness operations, recordkeeping and other functions. Moreover,automated record-keeping can facilitate repetitive operations wherebyGNSS-based guidance can be utilized for repeating guide paths, oradjusting as necessary. Moreover, records of operations can be utilizedfor quantitative record-keeping, such as volumes (cubic meters) ofmaterial handled, placement, updating topographical maps, 2-D/3-Dmodeling, etc. A data link 1372 can be provided from the equipmentcontrol subsystem 1304 to other mobile equipment 1306 in a fleet 1374for coordinating operations (FIG. 26).

As shown in FIG. 27, the snowcat or mobile equipment 1306 is adapted forsnow grooming operations, such as grading and shaping slopes with theadjustable snowplow 1340, the packing roller 1342 and other snowgrooming equipment. The equipment control subsystem 1304 for the mobileequipment 1306 can include the GNSS receiver 1312, the control computer1320, a steering controller 1358, a tool controller 1360 (e.g., for thesnowplow 1340 and the packing roller 1342) and an interface device 1362connecting the equipment control subsystem to the equipment. The vehiclesensor suite 1328 can include, without limitation, sensors for suchoperating parameters as steering angle, ground speed, videocapture/camera, fuel, engine RPM (tachometer), inertial measurement unit(IMU, e.g., accelerometers and gyroscopes) and tool parameters,designated 1376 a-g.

FIG. 28 shows an example of a screen display 1378 of the GUI/display(monitor) 1324, showing the snowcat or mobile equipment 1306 in agrooming operation covering an area generally designated 1380, which cancomprise an area of a ski resort or other facility utilizing mobileequipment for maintenance, grounds keeping, grooming, construction,earthmoving and other operations. Agricultural operations can also beaccommodated by the system 1302. The screen display 1378 generallyincludes a view area 1382, which shows a birds-eye view of theoperation, generally following the movement of the mobile equipment1306. Treatment guide paths or “swaths” 1384 are graphicallydistinguished from untreated areas 1386, e.g. by changing color or othergraphical treatments. The equipment guide path 1384 can include acenterline 1388, which is followed by the equipment 1306. The guidepaths 1384 and the centerlines 1388 can be preprogrammed, or generatedin real-time based on previous guide paths and such parameters asequipment width, equipment speed, terrain slope, snow depth, etc.

The screen display 1378 can include graphical display windows 1390around the view area 1382, which depict various aspects of theoperation, including equipment operating parameters, conditions, systemstatus and warning indicators. Vehicle speed can be displayed at 1392and vehicle heading (course) can be displayed at 1394. The display 1378can also include a superimposed steering/offset guide 1396, with anupper arc 1396 a indicating a steering direction and a lower, horizontalbaseline 1396 b showing an offset from a predetermined course. U.S. Pat.No. 6,539,303, incorporated herein by reference and assigned to a commonassignee herewith, shows a similar steering/offset guidance display. Thedisplay 1378 can include a directional arrow 1395 corresponding to adirection-of-travel for the vehicle/equipment 1306. The steering/offsetguidance display 1378 can be used for manually steering thevehicle/equipment 1306, or for monitoring the operation of anautosteering system. As shown in FIG. 28, terrain obstacles such as skilifts 1398 and a draw line 1399 can also be shown for assisting theoperator with avoiding such obstacles.

Another display 1402 is shown in FIG. 29 and includes “breadcrumb”trails 1404 with GNSS-defined marked points 1406 at predeterminedintervals along guide paths 1408. Such guidance and path-marking aredescribed above in connection with the antenna system 740 and are shownin FIG. 17. It will be appreciated that the displays 1378 and 1402 canbe selectively opened by the operator. Other displays can be utilizedwith appropriate emphasis on particular displays, graphics, dynamicequipment depictions, topographical mapping, operating parameters andother useful output information.

FIG. 30 shows another alternative embodiment of the present invention ina draw line system 1422. Such systems are particularly useful wheretopographies are relatively steep, such as advanced ski runs, andpresent difficulties for equipment designed to operate in groomingoperations. The draw line system 1422 includes an anchor post 1424anchoring a cable 1426 which is taken up on a reel 1428 mounted on thefront of the vehicle (i.e., snowcat) mounting grooming equipment 1338.

FIGS. 31-34 show a terrain modeling system 1462, which uses algorithmsfor interpolating snow depths. The terrain modeling system 1462 canutilize a mobile radar equipped system 1432, which can be mounted on avehicle such as a snow cat 1306. The radar equipped system 1432 caninclude an equipment control subsystem 1434 connected to aguidance/machine control computer 1320, a radar signal processingcomponent 1436, a transceiver 1438 and a transducer or antenna 1440. Theradar equipped system 1432 functions as a depth monitoring system 1452in the terrain modeling system 1462.

FIG. 32 shows a display 1454 with XY nodes 1456 corresponding to pointlocations on a topographical model. The nodes 1456 can also includeelevation, i.e. the Z component along a vertical axis in an XYZCartesian coordinate system. Contours 1458 corresponding to elevationscan be generated from the point elevations. As shown in FIG. 34, thedepths d (extrapolated) at points of interest or benchmarks 1470 can beextrapolated or interpolated from adjacent depths, such as d1 and d2based on distances dist1, dist2, dist3 and dist4 from the adjacent nodes1456 to a point of interest (benchmark) 1470.

FIGS. 31 and 34 are cross-sections of snow grooming operations showingan underlying earthen grade 1464, an existing snow base 1466 and snowfill 1468. Benchmarks 1464.1, 1466.1 and 1468.1 correspond to pointelevations at the earthen grade 1464, the existing snow base 1466 andthe fill 1468 respectively. For many operations these are the threeelevations of interest, for which the terrain modeling system 1462utilizes point elevations, i.e. XYZ coordinates in any suitable geodesicreference for purposes of creating topographical models.

Algorithms and software for computing such depths and generatingtopographical maps are well known in the field. For example, Surfercontouring, grading and 3-D surface mapping software is available fromGolden Software, Inc. (www.goldensoftware.com). Interpolation algorithmsare described in: Yang, C., “12 Different Interpolation Methods: a CaseStudy of Surfer 8.0;” Dressler, M., “Art of Surface Interpolation;” andBeutel, A. et al., “Natural Neighbor Interpolation-Based Grid DEMConstruction Using a GPU.” Other software and algorithms could also beused in connection with the terrain modeling system 1462. The terrainmodels generated can be output in suitable formats, including printouts,digital files, etc. Other functions include calculating material moved,workers' time records, equipment operating hours, etc.Previously-recorded terrain models can be archived for future reference,including prescriptions for future maintenance activity and saved guidepaths for vehicles.

FIG. 35 is a flowchart of a surface modeling method using approximationbased on scaling (ABOS), which interpolates point elevations andgenerates topographical models, including underlying terrain and snowdepths. From a start 1472, the method proceeds to filtering points at1474 based on their XYZ coordinates, for example, corresponding to theterrain model nodes 1456. A grid is specified at 1476, and maycorrespond to the grid 1455 (FIG. 33). Matrices are computed at 1478 anddefine the nodes 1456. Per partes interpolation occurs at 1480 and leadsto the method step of tensioning and smoothing the resulting matrix at1482, 1484. The matrix P is added to the new material, such as fill snowwith a resultant new matrix P at 1486. The f(X,Y) value is subtractedfrom the Z (altitude) value to provide the change in elevation DZ at1488, which is compared to the defined precision at 1490. If the maximumdifference DZ is greater than the defined precision (“YES” branch from1490) the process loops back to the interpolation step at 1482 to beginthe next iteration cycle. The cycles continue until DZ is less than thedefined precision, i.e. the resulting topographical model is accurate towithin the specified tolerances, whereat the method ends at 1492 (“NO”branch from 1490).

IX. Alternative Embodiment for Guiding Mine Trucks and Other Vehicles

FIG. 36 shows a vehicle control system 1442 comprising anotheralternative embodiment or aspect of the present invention. Withoutlimitation, an application of the control system 1442 is shown anddescribed on mine trucks 1444 traversing mine roads 1446. Suchoperations are often repetitive whereby routes are repeated and lendthemselves to automated guidance. As shown, the mine trucks 1444 can beautomatically guided to avoid each other and stay on course, even underlimited visibility conditions. Other aspects of the alternativeembodiments discussed above can be adapted to the system 1442.

X. Alternative Embodiment with Optical Sensors

FIG. 37 is a block diagram of a system 1502 comprising anotheralternative embodiment of the present invention for a tractor 1504pulling an implement 1506. The tractor 1504 mounts a camera 1508connected to and attitude processor 1510. Signals from the attitudeprocessor 1510 control a steering processor 1512, which in turn controlssteering actuators 1514. Optionally, artificial intelligence at 1516 canbe connected to the processor 1510. The implement 1506 includes multipleoptical sensors or targets 1518 mounted thereon. Roll/pitch/yawdirection sensors 1520 can comprise inertial measurement units, such asaccelerometers and gyroscopes.

FIGS. 38-39 show a crosshair display adapted for showing an implementorientation relative to a tractor orientation. Arrows in FIG. 39indicate a misalignment between the tractor and the implement. In otherwords, the tractor and implement are slightly yawed relative to eachother, which can be the result of field conditions or slight rollingmovements of the tractor and implement.

FIGS. 40-43 show square displays corresponding to the tractor and theimplement and indicating relative orientations. FIGS. 44-47 showcircular-elliptical target displays, which indicate misalignments andattitudes of the tractor and implement relative to each other. Forexample, the shape, orientation and size of the ellipses and their axesindicate relative attitudes and orientations of the tractor and theimplement relative to each other.

Such alignment and misalignment information can be processed andappropriate corrections implemented through the hitch connection andother control components. For example, cross track error can becompensated through a power hitch. Moreover, the alignment/misalignmentinformation can be processed to determine actual swath widths foraccurate field coverage.

IX. Conclusion

While the invention has been described with reference to exemplaryembodiments, it will be understood by those of ordinary skill in thepertinent art that various changes may be made and equivalents may besubstituted for the elements thereof without departing from the scope ofthe disclosure. In addition, numerous modifications may be made to adaptthe teachings of the disclosure to a particular object or situationwithout departing from the essential scope thereof. Therefore, it isintended that the claims not be limited to the particular embodimentsdisclosed as the currently preferred best modes contemplated forcarrying out the teachings herein, but that the claims shall cover allembodiments falling within the true scope and spirit of the disclosure.

The invention claimed is:
 1. A controller for steering a vehiclecomprising: one or more processors configured to: generate one or moresteering control commands to steer the vehicle to a desired position anda desired heading; measure a position and a heading for the vehicle inresponse to the steering control commands; compute a proportionality ofthe measured position to the desired position and a proportionality ofthe measured heading to the desired heading; and generate one or morecalibrated steering control commands based on the computedproportionality of the measured position to the desired position and thecomputed proportionality of the measured heading to the desired headingand a selectable operating parameter.
 2. The controller of claim 1,wherein the one or more processors repeatedly generate additionalcalibrated steering control commands based on computed proportionalitiesof measured positions of the vehicle to the desired position of thevehicle and computed proportionalities of measured headings of thevehicle to the desired heading until one of the measured positions ofthe vehicle is within a given range of the desired position.
 3. Thecontroller of claim 1, wherein the selectable operating parameter isselected by an operator.
 4. The controller of claim 1, wherein theselectable operating parameter is selected by the controller.
 5. Thecontroller of claim 1, wherein the selectable operating parametercomprises at least one of 3-D position, velocity, tilt, heading rate,rate of change of tilt angle, pitch, and radius of curvature of thevehicle.
 6. The controller of claim 1, wherein the one or morecalibrated steering control commands direct the vehicle toward thedesired position and heading to avoid crossing a desired track.
 7. Thecontroller of claim 1, the one or more processors further configured touse a recursive adaptive algorithm to generate the one or more steeringcontrol commands based on a response of the vehicle to one or more othersteering control commands.
 8. The controller of claim 1, the one or moreprocessors are further configured to: save a desired track for thevehicle; generate a deviation of the measured position and headingrelative to the desired track; and determine the one or more calibratedsteering control commands based on the deviation.
 9. The controller ofclaim 1, wherein the measured position and heading are based on signalsreceived from a global positioning system (GPS) receiver and agyroscope.
 10. The controller of claim 1, the one or more processors arefurther configured to send the one or more calibrated steering controlcommands to a steering controller to adjust operation of the vehicle oran implement operably coupled to the vehicle.
 11. A steering controllerfor a vehicle, comprising: at least one processing device; a memorystoring a recursive adaptive algorithm which, when executed by theprocessing device, cause the processing device to: generate one or moresteering control commands to turn the vehicle to a desired position,speed and attitude; measure a position, speed, and attitude of thevehicle turn in response to the steering control commands; calculate aproportionality of the measured position, speed, and attitude of thevehicle turn to the desired position, speed, and attitude of thevehicle; calculate one or more calibrated steering control commandsbased on the proportionality of the measured position, speed andattitude of the vehicle; and apply the one or more calibrated steeringcontrol commands to the steering controller to steer the vehicle. 12.The steering controller of claim 11, the processing device furtherconfigured to: calculate the calibrated steering control commands basedon a first proportionality factor times a difference between the desiredposition and the actual position and a second proportionality factortimes a difference between the desired attitude and the actual attitude.13. The steering controller of claim 12, wherein the measured positionand attitude are based on signals from a global navigation satellitesensor system (GNSS) receiver and a gyroscope on the vehicle.
 14. Thesteering controller of claim 11, wherein the steering controller isconfigured to attach to different vehicles or implements and determinethe one or more steering control commands based on one of the differentvehicles or implements to which the steering controller is attached. 15.The steering controller of claim 11, the processing device to determinethe one or more steering control commands based on a selectableoperating parameter including at least one of tilt, heading rate, rateof change of tilt angle, pitch, and radius of curvature of the vehicle.16. The steering controller of claim 11, the processing device to:measure a proportional rate of turn of the vehicle in response to theone or more steering control commands; and generate one or moreadditional steering control commands based, at least in part, on themeasured proportional rate of turn.